• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.12-12
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• 2010

By using scanning tunneling microscopy/spectroscopy (STM/S), we can make images of various physical properties in nanometer-scale spatial resolutions. Here, I demonstrate imaging of two electron-correlated subjects; screening and superconductivity by STM/S. The electrostatic potential around a charge is described with the Coulomb potential. When the charge is located in a metal, the potential is modified because of the free electrons in the host. The potential modification, called screening, is one of the fundamental phenomena in the condensed matter physics. Using low-temperature STM we have developed a method to measure electrostatic potential in high spatial and energy resolutions, and observed the potential around external charges screened by two-dimensional surface electronic states. Characteristic potential decay and the Friedel oscillation were clearly observed around the charges [1]. Superconductivity of nano-size materials, whose dimensions are comparable with the coherence length, is quite different from their bulk. We investigated superconductivity of ultra-thin Pb islands by directly measuring the superconducting gaps using STM. The obtained tunneling spectra exhibit a variation of zero bias conductance (ZBC) with a magnetic field, and spatial mappings of ZBC revealed the vortex formation [2]. Size dependence of the vortex formation will be discussed at the presentation.

• Bulletin of the Korean Chemical Society
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• v.21 no.6
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• pp.623-627
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• 2000

Aggregation of hydrophobically end-capped poly(ethylene oxide)s: HEURs, denoted as $C_8$$EO_{380}$$C_8$, $C_12$$CO_{600}$$C_{12}$, and $C_{18}$$EO_{860}$$C_{18}$,are described using static fluorescence, dynamic light scattering, and atomic force microscope (AFM) techniques. The CAC (critical aggregation concentration) was determined by com-paring two fluorescent peaks which were influenced by the polarity of the probe dye molecules, pyrene. The aggregation occurs in concentrations higher than 10 g/L of $C_8$$EO_{380}$$C_8$ and the CAC decreases by increasing the side chain length. The dynamic light scattering experiment shows fast mode and slow mode decays, and both are diffusive. The fast mode does not depend on the concentration, but the slow mode shows concentration dependence influenced by the formation of an aggregated structure. The hydrophobic end groups effect more dominantly than the main chains for the formation of HEUR micelles. By increasing the concentration, the HEUR micelles change their structure from spheres to rodlike micelles, and finally make fused structures, which were visualized with atomic force microscopy.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.19 no.5
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• pp.386-393
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• 2007

This paper studies the ventilation characteristics according to the jet fan location at the long road tunnel using the CFD software 'FLUENT' which is based on the finite volume method. The tunnel model used in the analysis has a length of 1600m, a cross sectional area of $120m^3$, and is composed of 3 lanes and one way. The velocity profile, the distribution of CO concentration and the ventilation flow rate within the tunnel are analyzed, respectively. In the analysis, it is found that the dependence of the ventilation flow rate upon the jet fan location is small, but the CO concentration in the tunnel is at the lowest when the jet fans are installed near the tunnel outlet. An air stream right below the jet fan is almost inactive due to the strong stream injection near the jet fan. Thus, the pollution level below the jet fan must be higher than the other area.

• Journal of the Optical Society of Korea
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• v.19 no.3
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• pp.272-276
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• 2015

The PbS quantum dot is an emerging photovoltaic material, which may provide high efficiency breakthroughs. The most crucial element for the high efficiency solar cells's development is to understand charge transport characteristics of PbS quantum dot solids, which are also important in planning strategic research. We have investigated charge transport characteristics of PbS quantum dot solids thin films using space charge limited conduction analysis and assessed thickness dependent photovoltaic performances. The extracted carrier drift mobility was $low-10^{-2}cm^2/Vs$ with the estimated diffusion length about 50 nm. These and recently reported values were compared with those from a commercial photovoltaic material, and we present an essential element in further development of PbS quantum dot solids materials.

• Mass Spectrometry Letters
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• v.10 no.2
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• pp.50-55
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• 2019

The fragmentation statistics of ion trap CID (Collision-Induced Dissociation) spectra using 87,661 tandem mass spectra of doubly charged tryptic peptides are analyzed here. In contrast to the usual method of using intensity information, the frequency of occurrence of fragment ions, with respect to the position of the cleavage site and the residues at these sites is studied in this paper. The analysis shows that the frequency of occurrence of fragment ion peaks is more towards the middle of the peptide than its ends. It was noted that amino acid with an aromatic and basic side chain at N- & C- terminal end of the peptide stimulates more peaks at the lower end of the spectrum. The residue pair effect was shown when the amide bond occurs between acidic and basic residues. The fragmentation at these sites (D/E-H/R/K) stimulates the generation of the y-ion peak. Also, the cleavage site H-H/R/K stimulates the generation of b-ions. K-P environment in the peptide sequence has more tendency to generate y-ions than b-ions. Statistical analysis helps in the visualization of the CID fragmentation pattern. Cleavage pattern along the length of the peptide and the residue pair effects, enhance the knowledge of fragmentation behavior, which is useful for the better interpretation of tandem mass spectra.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.32 no.1
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• pp.47-52
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• 2019

Micro-LEDs show lower efficiencies compared to general LEDs having large areas. Simulations were carried out using ray-tracing software to investigate the change in light extraction efficiency and light distribution according to chip-size of blue flip-chip micro-LEDs (FC ${\mu}-LEDs$). After fixing the height of the square FC ${\mu}-LED$ chip at $158{\mu}m$, the length of one side was varied, with dimensions of 2, 5, 10, 30, 50, 100, 300, and $500{\mu}m$. The highest light-extraction efficiency was obtained at $10{\mu}m$, beyond which the efficiency decreased as the chip-size increased. The chip size-dependence of the FC ${\mu}-LEDs$ both without the patterned sapphire substrate, as well as vertical FC ${\mu}-LEDs$, were analyzed.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.1
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• pp.34.2-34.2
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• 2019

Several observational results show a tighter pitch angle at wavelengths of optical and near-infrared than those that are associated with star formation, which is in agreement with the prediction of the density wave theory. In my recent numerical studies, the dependence of the shock positions relative to the potential minima is due to the tendency that stronger shocks form farther downstream. This causes a systematic variation of the perpendicular Mach number, with radius and makes the pitch angle of the gaseous arms smaller than that of the stellar arms, which supports the prediction of the density-wave theory, independently. However, some observations still give controversial results which show similar pitch angles at wavelengths, and there is no statistical study comparing observations and numerical models directly. By analyzing optical image of disk galaxies in the Carnegie-Irvine Galaxy Survey (CGS), I measured the physical values of stellar and gaseous arms such as their strength, length, and pitch angles. For direct comparison with numerical results, I analyzed more than 30 additional numerical models with varying the initial parameters in model galaxies. In this talk, I will present results both of observational and numerical samples and discuss the physical properties of spiral structures based on the density-wave theory.

• Progress in Superconductivity and Cryogenics
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• v.22 no.4
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• pp.20-23
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• 2020

Among many variables in processing the high performance MgB2 bulk superconductors, simple and important approach is to optimize the size dependence of the Mg & B raw powders. The present study is dedicated towards the variation in superconducting properties of MgB2 depending upon the various combination of Mg & B powders with the two different particle sizes respectively. From morphological investigation of the MgB2 samples, narrow and long pores are observed when the larger Mg powders are used, whereas it is rather like the oval shapes with the smaller Mg powders. Also, it can be seen that the connectivity of the MgB2 samples is much enhanced with the smaller size of the B powders. Jc-H properties of the MgB2 samples also indicate that the highest Jc can be obtained when using the smaller size of the B powder with the combination of the smaller Mg powders than that of the larger Mg powders. If the cases with the larger B powers, it is more favorable to select the larger Mg powders with the better Jc-H properties considering shorter diffusion length of Mg and more homogeneous mixture between the Mg & B powders.

• Journal of the Korean Society of Industry Convergence
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• v.25 no.2_1
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• pp.141-148
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• 2022

In this paper, the evaluation equations proposed by Tange et al. and Ando et al. were used to evaluate the threshold stress intensity factor ∆K^R_th(s) and fatigue limit ∆𝜎^R_wc, according to the small crack of offshore structural steel F690. Despite the differences in concept and shape of the two equations, the ∆K^R_th(s) and ∆𝜎^R_wc proved completely consistent. It is possible to use these equations to evaluate the dependence of the crack length on the ∆K^R_th(s) and ∆𝜎^R_wc of structures made of all steel grades. With these equations, the characteristics of microcracks can be quantitatively evaluated, and the safety and reliability of the structure can be secured.

• Journal of Intelligence and Information Systems
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• v.25 no.3
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• pp.161-177
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• 2019

In this paper, we study the performance improvement of the answer extraction in Question-Answering system by using sentence dependency parsing result. The Question-Answering (QA) system consists of query analysis, which is a method of analyzing the user's query, and answer extraction, which is a method to extract appropriate answers in the document. And various studies have been conducted on two methods. In order to improve the performance of answer extraction, it is necessary to accurately reflect the grammatical information of sentences. In Korean, because word order structure is free and omission of sentence components is frequent, dependency parsing is a good way to analyze Korean syntax. Therefore, in this study, we improved the performance of the answer extraction by adding the features generated by dependency parsing analysis to the inputs of the answer extraction model (Bidirectional LSTM-CRF). The process of generating the dependency graph embedding consists of the steps of generating the dependency graph from the dependency parsing result and learning the embedding of the graph. In this study, we compared the performance of the answer extraction model when inputting basic word features generated without the dependency parsing and the performance of the model when inputting the addition of the Eojeol tag feature and dependency graph embedding feature. Since dependency parsing is performed on a basic unit of an Eojeol, which is a component of sentences separated by a space, the tag information of the Eojeol can be obtained as a result of the dependency parsing. The Eojeol tag feature means the tag information of the Eojeol. The process of generating the dependency graph embedding consists of the steps of generating the dependency graph from the dependency parsing result and learning the embedding of the graph. From the dependency parsing result, a graph is generated from the Eojeol to the node, the dependency between the Eojeol to the edge, and the Eojeol tag to the node label. In this process, an undirected graph is generated or a directed graph is generated according to whether or not the dependency relation direction is considered. To obtain the embedding of the graph, we used Graph2Vec, which is a method of finding the embedding of the graph by the subgraphs constituting a graph. We can specify the maximum path length between nodes in the process of finding subgraphs of a graph. If the maximum path length between nodes is 1, graph embedding is generated only by direct dependency between Eojeol, and graph embedding is generated including indirect dependencies as the maximum path length between nodes becomes larger. In the experiment, the maximum path length between nodes is adjusted differently from 1 to 3 depending on whether direction of dependency is considered or not, and the performance of answer extraction is measured. Experimental results show that both Eojeol tag feature and dependency graph embedding feature improve the performance of answer extraction. In particular, considering the direction of the dependency relation and extracting the dependency graph generated with the maximum path length of 1 in the subgraph extraction process in Graph2Vec as the input of the model, the highest answer extraction performance was shown. As a result of these experiments, we concluded that it is better to take into account the direction of dependence and to consider only the direct connection rather than the indirect dependence between the words. The significance of this study is as follows. First, we improved the performance of answer extraction by adding features using dependency parsing results, taking into account the characteristics of Korean, which is free of word order structure and omission of sentence components. Second, we generated feature of dependency parsing result by learning - based graph embedding method without defining the pattern of dependency between Eojeol. Future research directions are as follows. In this study, the features generated as a result of the dependency parsing are applied only to the answer extraction model in order to grasp the meaning. However, in the future, if the performance is confirmed by applying the features to various natural language processing models such as sentiment analysis or name entity recognition, the validity of the features can be verified more accurately.