• Journal of the Korean Society of Visualization
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• v.21 no.1
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• pp.110-118
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• 2023

Characterizing the extensional rheological properties of non-Newtonian fluids is crucial in many industrial processes, such as inkjet printing, injection molding, and fiber engineering. However, educational institutions and research laboratories with budget constraints have limited access to an expensive commercial extensional rheometer. In this study, we developed a custom-made extensional rheometer using a CO₂ laser cutting machine and 3D printer. Furthermore, we utilized a smartphone with a low-cost microscopic lens for achieving a high spatial resolution of images. The aqueous polyethylene-oxide (PEO) solutions and a Boger fluid were prepared to characterize their extensional properties. A transition from a visco-capillary to an elasto-capillary regime was observed clearly through the developed rheometer. The extensional relaxation time and viscosity of the aqueous PEO solutions with a zero-shear viscosity of over 300 mPa·s could be quantified in the elasto-capillary regime. The extensional properties of the solutions with relatively small zero shear viscosity could be calculated using a smartphone's slow-motion feature with increasing temporal resolution of the images.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.37 no.5
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• pp.512-518
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• 2024

Titanium oxide (TiO₂), a representative photocatalyst, reacts to ultraviolet ray energy and has antibacterial, deodorizing, and antifouling properties using superhydrophilic properties, so it is widely used in various industrial fields such as environmental purification, building exterior walls, and road facilities. However, due to the nature of the photocatalyst, it reacts to ultraviolet rays known to be harmful to the human body, and is designed to react to natural light outdoors and to ultraviolet light sources inside a sealed device indoors, so indoor space is extremely limited. This study aims to develop spatial antibacterial technology for everyday living spaces by researching methods for antibacterial and deodorization by reacting titanium oxide (TiO₂)-based photocatalysts with the visible light range emitted from lighting devices in everyday spaces. Through the results of this study, it was verified through experiments that the photocatalyst exhibits antibacterial and deodorizing properties in response to lighting devices (LED, fluorescent lights, etc.) used in daily life. Based on the research results, we hope that various studies will be conducted to create a safer living environment by applying this technology to various fields such as large-scale complex facilities where an unspecified number of floating populations gather, airports, port waiting rooms, and public transportation.

• Journal of the Korean Geographical Society
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• v.40 no.2 s.107
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• pp.221-241
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• 2005

Land Use and Land Cover Changes (LUCC) occur over a wide range of space and time scales, and involve complex natural, socio-economic, and institutional processes. Therefore, modelling and predicting LUCC demands an understanding of how various measured properties behave when considered at different scales. Understanding spatial and temporal variability of driving forces and constraints on LUCC is central to understanding the scaling issues. This paper aims to 1) assess the heterogeneity of land cover change processes over the landscape in northern Ghana, where intensification of agricultural activities has been the dominant land cover change process during the past 15 years, 2) characterise dominant land cover change mechanisms for various spatial scales, and 3) identify the optimal spatial scale for LUCC modelling in a savanna landscape. A multivariate statistical method was first applied to identify land cover change intensity (LCCI), using four time-sequenced NDVI images derived from LANDSAT scenes. Three proxy land use change predictors: distance from roads, distance from surface water bodies, and a terrain characterisation index, were regressed against the LCCI using a multi-scale hierarchical adaptive model to identify scale dependency and spatial heterogeneity of LUCC processes. High spatial associations between the LCCI and land use change predictors were mostly limited to moving windows smaller than 10$\times$10km. With increasing window size, LUCC processes within the window tend to be too diverse to establish clear trends, because changes in one part of the window are compensated elsewhere. This results in a reduced correlation between LCCI and land use change predictors at a coarser spatial extent. The spatial coverage of 5-l0km is incidentally equivalent to a village or community area in the study region. In order to reduce spatial variability of land use change processes for regional or national level LUCC modelling, we suggest that the village level is the optimal spatial investigation unit in this savanna landscape.

• ETRI Journal
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• v.38 no.4
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• pp.634-644
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• 2016

Channel-based radio-frequency fingerprinting such as a channel impulse response (CIR), channel transfer function (CTF), and frequency coherence function (FCF) have been recently proposed to improve the accuracy at the physical layer; however, their empirical performance, advantages, and limitations have not been well reported. This paper provides a comprehensive empirical performance evaluation of RF location fingerprinting, focusing on a comparison of received-signal strength, CIR-, CTF-, and FCF-based fingerprinting using the weighted k-nearest neighbor pattern recognition technique. Frequency domain channel measurements in the IEEE 802.11 band taken on a university campus were used to evaluate the accuracy of the fingerprinting types and their robustness to human-induced motion perturbations of the channel. The localization performance was analyzed, and the results are described using the spatial and temporal radio propagation characteristics. In particular, we introduce the coherence region to explain the spatial properties and investigate the impact of the Doppler spread in time-varying channels on the time coherence of RF fingerprint structures.

• Spatial Information Research
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• v.15 no.4
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• pp.397-406
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• 2007

2D hydraulic models of urban areas are at the forefront of current research of flood inundation mechanisms, but they are constrained by inadequate parameters of topography and insufficient data. In this paper a numerical model based on DEMs is presented to represent overflow waters due to bank break in urban areas. The surface flow in the building areas is assumed to be properly modeled by solving Saint-Venant equation. In order to represent flooding broken out in Samcheok city, 2002, hydraulic model test using tracer has been carried out and validated. These efforts will serve for making flood hazard map and for estimating economic loss due to inundation of personal properties in urban areas.

• Geomechanics and Engineering
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• v.23 no.3
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• pp.207-215
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• 2020

This paper presents a kinematic limit analysis for passive earth pressure of rigid retaining structures considering the unsaturation of the backfill. Particular emphasis in the current work is focused on the effects of the spatial change in the degree of saturation on the passive earth pressure under different steady-infiltration/evaporation conditions. The incorporation of change of effective unit weight with degree of saturation is the main contribution of this study. The problem is formulated based on the log-spiral failure model rather than the linear wedge failure model, in which both the spatial variations of suction and soil effective unit weight are taken into account. Parametric studies, which cover a wide range of flow conditions, soil types and properties, wall batter, back slope angle as well as the interface friction angle, are performed to investigate the effects of these factors on the passive pressure and the corresponding shape of potential failure surfaces in the backfill. The results reveal that the flow conditions have significant effects on the suction and unit weight of the clayey backfill, and hence greatly impact the passive earth pressure of retaining structures. It is expected that present study could provide an insight into evaluation of the passive earth pressure of retaining structures with unsaturated backfills.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.105.1-105.1
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• 2016

Many of the complex materials developed today derive their unique properties from the presence of multiple phases or from local variations in elemental concentration. Simply performing analysis of the bulk materials is not sufficient to achieve a true understanding of their physical and chemical natures. Secondary ion mass spectrometer (SIMS) has met with a great deal of success in material characterization. The basis of SIMS is the use of a focused ion beam to erode sample atoms from the selected region. The atoms undergo a charge exchange with their local environment, resulting in their conversion to positive and negative secondary ions. The mass spectrometric analysis of these secondary ions is a robust method capable of identifying elemental distribution from hydrogen to uranium with detectability of the parts per million (ppm) or parts per billion (ppb) in atomic range. Nano secondary ion mass spectrometer (Nano SIMS, Cameca Nano-SIMS 50) equipped with the reactive ion such as a cesium gun and duoplasmatron gun has a spatial resolution of 50 nm which is much smaller than other SIMS. Therefore, Nano SIMS is a very valuable tool to map the spatial distribution of elements on the surface of various materials In this talk, the surface imaging applications of Nano SIMS in KBSI will be presented.

• Journal of the Korean Institute of Landscape Architecture
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• v.19 no.2
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• pp.75-91
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• 1991

This study is one of studies on the analysis of vegetation spatial image and visual preference of roadside slopes in Chi-Ri Mt. national park. In this article, we analized the soil characteristics and the actual vegetation within slopes and forest lands contiguous to those. The results obtained were summarized as follows; The physical and chemical properties of soil in forest lands were better than slopes and Cheoneun temple - Seongsam pass was the best fertilized among 3 sector. In the structure of woody plants in forest lands, the high importance value species were Pinus denciflora, Quercus aliena within Ukmojeong-Deokdong sector, Q. aliena, Q. varabilis, Q. serrata within Banseon-Seongsam pass sector, and P. denciflora, Q. dentata within Cheoneun temple-Seongsam pass sector. And also, Aster scaber, Arundinella hirta, Pteridium aquilinum were the high importance value herbs within all sector. In slopes, the species diversity indices of woody plants were low, but that of herbs showed slightly high. By the cluster analysis used in similarity index, it was observed that woody plants structure between slopes and forest lands made little, but the herbs made slightly higher than woody plants.

• Korean Journal of Optics and Photonics
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• v.13 no.1
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• pp.44-50
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• 2002

A new wavelength demultiplexing scheme using holographic volume phase grating formed in photopolymer is proposed and demonstrated. Through the analysis and experiments of the design parameters such as wavelength selectivity, operating spectral range, spatial channel distance and spatial intensity distribution of each channel, we proved that the proposed demultiplexing scheme is promising for wavelength division multiplexing (WDM). From the experimental results, the 3 dB bandwidth of 0.21nm and the crosstalk level of 26 dB for a 0.8 nm channel spacing are observed.

• The Korean Journal of Ecology
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• v.20 no.6
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• pp.451-459
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• 1997

Seasonal and spatial distribution of vascular plants were examined and related to soil texture, pH, moisture and nutrient contents in the riparian zone of the Balan Stream. In spring the area was dominated by Alopecurus aequalis var. amurensis, was displaced by Persicaria thunbergii and Humulus japonicus in summer. From the stream channel to bank, soil texture and pH were not significantly differentiated, moisture decreased, organic matter and K increased, and TKN and available P increased in June and decreased in August. DCA ordination analysis by species distribution showed spatially and seasonally distinct patterns seasonal difference was evident on axis 1, and spatial difference according to the distance from stream channel was clear, too. Both axis 1 and axis 2 scores were significantly correlated with biomass, pH, and phosphate. Species richness increased were significantly correlated with biomass, pH, and phosphate. Species richness increaed with increasing organic matter and phosphate, and decreased with increasing soil moisture and K. Biomass increased with increasing organic matter, but was negatively related to pH, moisture, TKN, available P and K. Available P was significantly correlated with biomass, pH, and total soil nitrogen. In conclusion, the distribution of riparian vegetation was governed by soil physico-chemical properties, which are primarily determined by how far it is from the stream channel.