343 research outputs found
복수 우변 벡터를 갖는 선형 계획 문제에 관한 해법 연구
No full text학위논문(석사) - 한국과학기술원 : 경영과학과, 1986.2, [ [ii], 38 p. ; ]The purpose of this thesis is to give a solution method for the multiple right-hand choice linear programming problem which was first studied by E.L. Johnson in 1974. The algorithm presented in this thesis is based on cross decomposition method developed by Van Roy that unified Benders decomposition and Lagrangian relaxation into a single framework. In our problem, Benders subproblem turns out to be a linear programming problem and Lagrangian subproblem is decomposed into a LP problem and a trivial integer programming problem. The algorithm suggested in this thesis exploits the special structures of the multiple right-hand choice LP problem. Computational results are given for 30 test problems.한국과학기술원 : 경영과학과
경사진 실리콘(100) 표면과 5쪽 원소와의 상호작용 그리고 반경험적 포텐셜을 이용한 금속표면과 금속뭉치에 대한 몬테칼로 연구
No full text학위논문(박사) - 한국과학기술원 : 화학과, 1999.2, [ xix, 226 p. ][Chapter Ⅰ. Atomic-step Rearrangement on Si(100)by Interaction with Antimony]
We have observed the various step structures of Sb : Si(100) surfaces with a miscut of 2°by controlling kinetics and thermodynamics. In the kinetic regime of 375 K the 2×1 single-domain or the 1×2 one was observed depending on Sb coverage, while in a thermodynamic regime above 900 K the double-domain with symmetric domain population is observed. Also, the 1×2 surface has undergone the successive structural phase transition from the (2×1) to the (2×2) and the (2×2) to the c(4×4) phase as the 1×2 surface was annealed at 1200 K. These successive structural phase transitions are irreversible. The single-domain formation was explained by the vacancy mediated mixing model, which can explain consistently the unexpected coverage of 1.4 ML of 1×2 single-domain at low temperature and the c(4×4) reconstruction. The symmetric double-domain structure was discussed based on the anisotropic stress tensor and the elimination of rebond by displacing the Si atom with Sb at the step. Surface mixing, anisotropic stress, and the elimination of the rebond at the step are expected to be the main causes of the observed domain structures and reconstructions.
[Chapter Ⅱ. Reconstructions and Step Structures on Vicinal Si(100) surfaces by Interaction with Bi]
Reconstructions and step structures on vicinal Si(100) surfaces by interaction with Bi are studied under diverse experimental conditions with varying substrate temperatures and Bi coverages. The various reconstructions and the step structures on Bi:Si(100) are observed depending on the substrate temperatures and Bi coverages. At low coverages, (2×2) and c(4×4) phase are observed below 350 K and at about 400 K, respectively. For the saturated surfaces, (2×1) and high order (2×7) phase are observed below 400 K and at 500~800 K, respectively. Comparing the formation temperatures for each phase, it can be concluded that the c(4×4) structure has en...한국과학기술원 : 화학과
Hydrothermal Synthesis of Composition- and Morphology-Tunable Polyimide-Based Microparticles
No full textPolyimide
is one of the most important high-performance polymers,
which is widely used due to its excellent mechanical performance and
thermal stability. Unlike the conventional synthetic approach, hydrothermal
polymerization enables the synthesis of polyimides without any toxic
solvent and catalyst. Herein, we report the synthesis of polyimide-based
microparticles (PIMs) through one-pot hydrothermal polymerization
using precursors of mellitic acid (MA) and three isomers of phenylenediamine
(PDA) (o-, m-, and p-PDA). Interestingly, the chemical composition of PIMs was highly
tunable with the choice of the PDA isomers, leading to considerable
morphological differences between PIMs. The molecular dynamics simulation
and density functional theory calculation of the polymeric segment
of the respective PIMs suggested that the relative ratio of amide
to imide influenced the rotational freedom of the polymeric chains
and number of hydrogen bonds, resulting in the well-defined structures
of respective PIMs. Considering the highly tunable nature of PIMs
coupled with the facile synthetic protocol, we anticipate prospective
potentials of PIMs in materials, energy, and composite applications
Hydrogen-Bond Free Energy of Local Biological Water
No full textHere, we propose an experimental methodology based on femtosecond???resolved fluorescence spectroscopy to measure the hydrogen (H)???bond free energy of water at protein surfaces under isothermal conditions. A demonstration was conducted by installing a non???canonical isostere of tryptophan (7???azatryptophan) at the surface of a coiled???coil protein to exploit the photoinduced proton transfer of its chromophoric moiety, 7???azaindole. The H???bond free energy of such biological water was evaluated by comparing the rates of the proton transfer, sensitive to the hydration environment, at the protein surface and in bulk water, and it was found to be higher than that of bulk water by 0.4 kcal/mol. The free???energy difference is dominated by the entropic cost in the H???bond network among water molecules at the hydrophilic and charged protein surface. Our study opens a door to accessing the energetics and dynamics of local biological water to give insight its roles in protein structure and function
????????? ??????????????? ?????? ????????? ????????? ????????? ??? ?????? ?????? ??????????????? ?????? ????????? ??????
No full textSchool of Energy and Chemical Engineering (Chemical Engineering)Rechargeable batteries have attracted a lot of attention owing to their wide applicability, such as portable/consumer electronics, electric vehicles, and grid-scale applications. Over the past two decades, significant advances have been made in battery technologies. However, advancement in various technologies necessitates batteries that are more efficient because the current levels of performance are inadequate. This has encouraged researchers to design and discover new battery materials to meet future demands. In this context, a fundamental understanding of the polymorphism and charge storage mechanism of battery materials can provide design principles and promote the discovery of novel materials. To achieve this, the multiscale simulation method has been used to study physicochemical phenomena or properties of different time and space scales. In this dissertation, we introduced theoretical studies on polymorphism and charge storage mechanism of battery materials. Specifically, we discussed three newly designed electrode materials, a conventional binder material, and a separator material.
In Chapter 1, we provide an overview and the challenges of rechargeable batteries. We then present a general background of the charge storage mechanism and polymorphism phenomenon and their importance in the study and design of rechargeable battery materials. Finally, we describe the modern multiscale computational techniques for rechargeable battery materials such as the density functional theory calculation, density functional tight binding calculation, molecular dynamics simulation, and Monte Carlo simulation.
In Chapter 2, we present a theoretical study on the polymorphism and charge storage mechanism of contorted hexabenzocoronene (c-HBC) as a new type of anode material for Li-ion batteries. In this study, the packing polymorphism was demonstrated by disclosing the crystal structure of polymorph ??????, which is the metastable R-3 crystal phase, using computational polymorph prediction. It was also revealed that polymorph ??? was not a polymorph of c-HBCinstead, it is the P31 (or P32) crystal phase of c-HBC with Pd atoms. Moreover, our investigation on the lithium storage mechanism showed that the c-HBC anode exhibited a single-stage Li-ion insertion behavior without voltage penalty, which was attributed to the 3D-ordered empty pores originating from the contorted structure of c-HBC.
In Chapter 3, we present a theoretical study on the polymorphism and charge storage mechanism of fluorinated-contorted hexabenzocoronene (F-cHBC) as a potential electrochemical organic electrode material. Based on Monte Carlo computational study, it was revealed that the crystal structure of polymorph I was the energetically stable P21/c crystal phase. Furthermore, theoretical investigation on lithium/sodium storage mechanism showed that Li- and Na-ions could be stored in two distinct sites surrounded by electronegative fluorine atoms and a negatively charged bent edge aromatic ring.
In Chapter 4, we present a theoretical study on the polymorphism and charge storage mechanism of the redox-active covalent triazine framework (rCTF) as a promising organic anode material for Li-ion batteries. The potential energy analysis suggested that the rCTF can potentially exhibit packing polymorphism for two energy-minimum packing modes, namely, AB and slipped-parallel packing modes. The most stable was the slipped-packing mode. Furthermore, we revealed that the rCTF provided a theoretical capacity of up to 1200 mAh g???1 using quinone, triazine, and benzene rings as the redox-active sites. The structural deformation of rCTF during activation allowed more redox-active sites to be accessible, especially the benzene rings.
In Chapter 5, we present a theoretical study on poly(vinylidene fluoride) (PVDF), which is a conventional polymeric binder material for rechargeable batteries. Although it is rarely considered in the battery field, PVDF is a semicrystalline polymer with various polymorphs that have different polarization characteristics. In this study, the effect of the crystal phases of PVDF, specifically ??- and ??-PVDFs, on battery performance was investigated. We showed that compared to negligible polarization of the paraelectric ??-PVDF, the strong polarization generated by the ferroelectric ??-PVDF can effectively transport electrons and Li-ions, leading to reduction in the charge transfer resistance and mitigation of the concentration polarization in the Li-ion battery system.
In Chapter 6, we present a theoretical study on polymorphism of chitin separator material and its interaction with electrolyte. As a semicrystalline biopolymer, chitin can exist in two polymorphs, ??- and ??-phase. These crystals have different molecular conformation and arrangement, resulting in different polarization characteristics. Based on density functional theory calculations and molecular dynamics simulations, we revealed that both polymorphs of chitin had excellent electrolyte-uptaking property and high physicochemical affinity to Li-ions with binding reversibility.ope
Mesenchymal Stromal Cells Inhibit Inflammatory Lymphangiogenesis in the Cornea by Suppressing Macrophage in a TSG-6-Dependent Manner
No full textThe cornea is a transparent tissue devoid of blood and lymphatic vessels. However, various inflammatory conditions can cause hemangiogenesis and lymphangiogenesis in the cornea, compromising transparency and visual acuity. Mesenchymal stem/stromal cells (MSCs) have therapeutic potentials in a variety of diseases because of anti-inflammatory proper- ties. Herein, we investigated the effects of MSCs on corneal angiogenesis using a model of suture-induced inflammatory corneal neovascularization. Data demonstrated that an intravenous administration of MSCs suppressed corneal inflammation and neovascularization, inhibiting both hemangiogenesis and lymphangiogenesis. MSCs reduced the levels of vascular endothelial growth factor (VEGF)-C, VEGF-D, Tek, MRC1, and MRC2 in the cornea, which are expressed by pro-angiogenic macrophages. Moreover, the number of CD11b(+) monocytes/macrophages in the cornea, spleen, peripheral blood, and draining lymph nodes was decreased by MSCs. Depletion of circulating CD11b(+) monocytes by blocking antibodies replicated the effects of MSCs. Importantly, knockdown of tumor necrosis factor alpha (TNF-alpha)-stimulated gene/protein 6 (TSG-6) in MSCs abrogated the effects of MSCs in inhibiting corneal hemangiogenesis and lymphangiogenesis and monocyte/macrophage infiltration. Together, the results suggest that MSCs inhibit inflammatory neovascularization in the cornea by suppressing pro-angiogenic monocyte/macrophage recruitment in a TSG-6-dependent manner.N
Biomimetic Superoxide Disproportionation Catalyst for Anti-Aging Lithium???Oxygen Batteries
No full textReactive oxygen species or superoxide (O2???), which damages or ages biological cells, is generated during metabolic pathways using oxygen as an electron acceptor in biological systems. Superoxide dismutase (SOD) protects cells from superoxide-triggered apoptosis by converting superoxide to oxygen and peroxide. Lithium???oxygen battery (LOB) cells have the same aging problems caused by superoxide-triggered side reactions. We transplanted the function of SOD of biological systems into LOB cells. Malonic acid-decorated fullerene (MA-C60) was used as a superoxide disproportionation chemocatalyst mimicking the function of SOD. As expected, MA-C60 as the superoxide scavenger improved capacity retention along charge/discharge cycles successfully. A LOB cell that failed to provide a meaningful capacity just after several cycles at high current (0.5 mA cm???2) with 0.5 mAh cm???2 cutoff survived up to 50 cycles after MA-C60 was introduced to the electrolyte. Moreover, the SOD-mimetic catalyst increased capacity, e.g., more than a 6-fold increase at 0.2 mA cm???2. The experimentally observed toroidal morphology of the final discharge product of oxygen reduction (Li2O2) and density functional theory calculation confirmed that the solution mechanism of Li2O2 formation, more beneficial than the surface mechanism from the capacity-gain standpoint, was preferred in the presence of MA-C60
METHOD FOR TRANSMITTING/RECEIVING DATA IN COMMUNICATION SYSTEM
No full textDisclosed is a method and system for transmitting and receiving data in a communication system. The system includes a base station, and a relay station connecting the base station with at least one mobile station. The base station transmits data for a plurality of mobile stations to the relay station, and transmits the data to at least one mobile station belonging to the base station from among the plurality of mobile stations. The relay station receives the data from the base station, and transmits the data to at least one mobile station belonging to the relay station from among the plurality of mobile stations in the same interval as an interval where the base station transmits the data to the mobile station
Structural, Electronic and Magnetic Properties of Radical-based 2D Covalent Organic Frameworks
No full textWe designed radical-based two-dimensional (2D) covalent organic framework using tris(2,3,5,6-tetrachlorophenyl)methyl radical building block. We considered four possible AA and AB stacking structures of the radical-based 2D COF and investigated the structural, electronic and magnetic properties. The interlayer distance of the radical-based 2D COF depended on the stacking structure and contact type. The contact between radical building blocks was found to increase the interlayer distance. Also, the thermodynamic stability of the radical-based 2D COF was found to increase as its interlayer distance decreases. The density of states of the radical-based 2D COF showed a finite band gap with intermediate energy levels between the gap. The energy states near Fermi level was mainly occupied by pz orbitals of carbon atoms. The magnetization due to the radical center of the 2D COF was also observed. The magnetic moment of the radical center was in the range of 0.27-0.30, indicating that the unpaired electron of carbon atom was not localized in the radical center
Direct Growth of Bi2SeO5 Thin Films for High-k Dielectrics via Atomic Layer Deposition
No full textThis study describes a modified atomic layer deposition (ALD) process for fabricating BiO x Se y thin films, targeting their application as high-k dielectrics in semiconductor devices, especially for two-dimensional semiconductors. Using an intermediate-enhanced ALD technique for Bi2Se3 and a plasma-enhanced ALD process for Bi2O3, a method for the sequential deposition of Bi2SeO5 ternary films has been established. The thin film has been deposited on SiO2 and TiN substrates, exhibiting growth rates of 0.17 to 0.16 nm<middle dot>cycle-1 without an incubation period, thanks to facile nucleation characteristics. The resulting film exhibited high flatness and reached 96% of its theoretical density, forming a uniform nanocrystalline structure. Electrical evaluations using metal-insulator-metal capacitors indicated the dielectric constant (similar to 17.6) and electrical breakdown strength (2.6 MV<middle dot>cm-1), demonstrating their potential as a dielectric layer.
- …
