• Polymer(Korea)
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• v.26 no.2
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• pp.168-173
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• 2002

Poly (vinyl butyral) (PVB) was synthesized by acetalization of poly (vinyl alcohol) (PVA) PVB was prepared in particulate forms in water, and chemical and physical properties of the products were characterized using various techniques. The prepared PVB had size distribution from 100 to 700 $\mu\textrm{m}$ with mean diameter of about 380 $\mu\textrm{m}$. The chemical structure of PVB was characterized using FT/IR and NMR, and the average degree of acetalization was determined to be 77% from the titration measurement. DSC data showed that the crystalline structure of PVA vanished as acetalization reaction proceeded to produce PVB, and the glass transition temperature emerged at about $70^{\circ}C$. TGA data showed that PVB was much more thermally stable than PVA, and showed no degradation up to $300^{\circ}C$. Solubility test showed that PVB was soluble in alcohols but Insoluble in water, being totally different from PVA.

• Journal of Korean Society of Steel Construction
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• v.15 no.3
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• pp.331-339
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• 2003

The study discussed in this paper investigated the material characteristics for the Thermo-Mechanical Control Process(TMCP) plates, which are controlled by several factors such as rolling, cold-stripping, cooling rate, and fixed carbon quantity. The suitability of thick TMCP steel plates as structural steel was also estimated through several experiments and with the us of a statistical method to analyze mill certificate sheets provided by the manufacturer. The results of this study are as follows: the TMCP steel plates showed stable values of the composition parameter ($P_cm$) and the carbon equivalents ($C_eq$ ) with satisfied yield strength, ultimate strength, and low-yield ratio.

• Smart Media Journal
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• v.10 no.2
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• pp.110-118
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• 2021

The Internet of Things (IoT) technology, a key growth engine of the 4th industrial revolution, has grown to a stage where it can autonomously communicate with each other and process data according to space and circumstances. Accordingly, the IT infrastructure becomes increasingly complex and the importance of the monitoring field for maintaining the system stably is increasing. Monitoring technology has been used in the past, but there is a need to find a flexible monitoring system that can respond to the rapidly changing ICT technology. This paper conducts research on designing and testing an open source-based Prometheus monitoring system. We builds a simple infrastructure based on IoT devices and collects data about devices through the Exporter. Prometheus collects data based on pull and then integrates into one dashboard using Grafana and visualizes data to monitor device information.

• The Journal of Engineering Geology
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• v.18 no.1
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• pp.55-68
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• 2008

At present underground structures such as road tunnels, railway tunnels, underground petroleum storages and radioactive waste storages are being constructed in numerous places in Korea. For the construction of underground structrues, it should be accounted for natural factors (geology, hydrogeology, soil, vegetation, topography and drainage patterns) and human-social factors (land use, urbanization, population, culture and transportation). Especially, hydrogeology should be regarded as an important factor for evaluating the safety of underground structures and their impact to groundwater system around the structures. This study aimed to recognize hydrogeological characteristics of shallow formations in the area from Dongrae crossway to Seo-Dong where 45 boreholes were drilled for the construction of Line-3 subway in Busan Megacity. Slug tests for unsaturated and saturated zones were conducted on 30 boreholes in the study area. From the result of the slug tests, it was identified that average zonal hydraulic conductivity in the unsaturated zone was higher than that in the saturated zone. Besides, the slug test result in the saturated zones may reflect hydraulic properties of the upper most part of the saturated zones.

• The Korean Journal of Financial Management
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• v.21 no.1
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• pp.149-181
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• 2004

In this study we perform empirical tests using KOSPI return to investigate the existence of nonlinear characteristics in the generating process of stock returns. There are three categories in empirical tests; the test of nonlinear dependence, nonlinear stochastic process and nonlinear deterministic chaos. According to the analysis of nonlinearity, stock returns are not normally distributed but leptokurtic, and appear to have nonlinear dependence. And it's decided that the nonlinear structure of stock returns can not be completely explained using nonlinear stochastic models of ARCH-type. Nonlinear deterministic chaos system is the feedback system, which the past incidents influence the present, and it is the fractal structure with self-similarity and has the sensitive dependence on initial conditions. To summarize the results of chaos analysis for KOSPI return, it is the persistent time series, which is not IID and has long memory, takes biased random walk, and is estimated to be fractal distribution. Also correlation dimension, as the approximation of fractal dimension, converged stably within 3 and 4, and maximum Lyapunov exponent has positive value. This suggests that chaotic attractor and the sensitive dependence on initial conditions exist in stock returns. These results fit into the characteristics of chaos system. Therefore it's decided that the generating process of stock returns has nonlinear deterministic structure and follow chaotic process.

• Proceedings of the KWS Conference
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• 2010.05a
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• pp.73-73
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• 2010

합금원소가 다량 첨가된 고합금강, 스테인리스강, Ni기 초내열합금 등은 용접시 혹은 후열처리 동안 열영향부 (HAZ: heat-affected-zone)에서 결정립계를 따라서 액화균열이 종종 발생한다. 이러한 액화균열은 급속한 가열시 HAZ의 결정립계가 국부적으로 용융되어 액상필름을 형성하고, 냉각시 수축으로 인한 인장구속응력에 의해 필름을 따라서 균열이 발생하여 생성된다. HAZ 결정립계 액화는 탄화물, 황화물, 인화물, 보론계 화합물 등이 급가열시 기지와의 반응에 의해 표피 액상을 형성하는 조성적 액화 (constitutional liquation)에 의한 액상의 결정립계 침투로 설명되거나, 결정립계 자체의 용융점을 상당량 낮추는 보론(B), 인(P), 황(S)등의 편석에 의한 국부적 입계 용융으로 주로 연관 지어 해석한다. HAZ 액화균열은 고온 입계균열 현상이므로, 결정립계의 특성에 따라 크게 영향을 받으며 결정립계 character 설계에 의해 액화균열 저항성을 개선시킬 수 있음을 유추할 수 있다. 한편, 본 연구자들은 최근 Ni기 초내열합금에 있어 입계 serration 현상을 새롭게 발견하였으며, 이론적 접근법을 통해 serration을 위한 특별한 열처리 방법을 개발하였다. 형성된 파형입계는 결정학적인 관점에서 조밀 {111} 입계면을 갖도록 분해 (dissociation)되어 낮은 계면에너지를 갖게 됨을 확인하였으며, 입계형상 변화뿐만 아니라 탄화물 특성변화까지 유도하여 크리프 수명을 기존대비 약 40% 정도 향상시킴을 확인하였다. 본 연구에서는 이러한 직선형 입계 대비 'special boundary'로 간주되는 파형입계가 도입될 경우, 보론 편석 및 HAZ 액화거동에 미치는 영향을 고찰하고자 하였다. SIMS (secondary ion mass spectrometry)를 이용하여 열처리 직후 결정립계 보론편석 정도를 비교하였다. 파형입계 시편의 경우, 일반직선형 시편에 비해 결정립계에 보론편석 저항성이 우수함을 확인할 수 있었다. 재현 HAZ 열사이클 시험을 통해 미세조직을 정량적으로 분석하였다. 파형입계 시편 및 일반직선형 시편 모두 최고온도 $1060^{\circ}C$이상부터 입계 탄화물이 기지내로 완전 용해되고 입계가 액화되기 시작하였다. 최고온도별로 입계액화비율을 정량적으로 비교한 결과, 파형입계가 직선입계 대비 훨씬 낮음을 확인할 수 있었으며, 때때로 액화된 필름이 입계를 따라 전파되지 않고 부분적으로 단락되어 있음이 관찰되었다. 액화시험 후 투과전자현미경을 이용한 EDS (energy dispersive spectrometry) 분석을 통해 결정립계 액화의 주요원인은 입계 $M_{23}C_6$의 조성적 액화반응 보다는 보론 편석 (원자 및 $M_{23}(CB)_6$)으로 인한 결정립계 국부용융이 더 유력함을 유추할 수 있었다. 따라서 상기 결과로부터 입계구조가 안정되어 계면에너지가 낮은 파형입계가 보론편석에 대한 저항성이 우수하였으며, 이러한 결과는 액화 저항성에 대응되어 영향을 미침을 알 수 있었다. 게다가 파형입계에 액상 필름이 생성되더라도 낮은 계면에너지에 의해 비롯된 상대적으로 낮은 적심성 (wettability)에 의해 필름이 쉽게 전파되지 않음을 'Smith 입계 wetting 이론'을 이용하여 해석할 수 있었다.

• Journal of Sensor Science and Technology
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• v.11 no.6
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• pp.350-357
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• 2002

Micro gas sensor with single electrode was proposed for improving stability and sensitivity. Generally, metal oxide gas sensors have two electrodes for heating and sensing. This fabricated new type sensor have only a single electrode by forming a sensing material onto heating electrode. Pt as a heating and sensing electrode was sputtered on glass substrate and a $SnO_2$ sensing material was thermally evaporated on Pt electrode. $SnO_2$ was patterned by lift-off process and then thermally oxidized in $O_2$ condition for 1 hr., $600^{\circ}C$. The size of fabricated sensor was $1.9{\times}2.1\;mm^2$. As a result of CO gas sensing characteristics, this sensor showed 100 mV change for 1,000 ppm and linearity for wide range($0{\sim}10,000\;ppm$) of gas concentrations. And the sensor shows a good recovery characteristics of 1% deviation compared to initial resistance.

• Polymer(Korea)
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• v.36 no.3
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• pp.275-280
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• 2012

Poly(amic acid)s were successfully synthesized from 1,4-bis(4-aminophenoxy)benzene (1,4-APB) or 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (HFBAPP) with pyromellitic dianhydride (PMDA), 3,3'-4,4'-benzopenonetetracarboxylic dianhydride (BPDA) and $p$-phenylenediamine ($p$-PDA) and then they were effectively converted into polyimide films by thermal imidization. The chemical structure and thermo-mechanical properties of polyimide films were examined using Fourier transform infrared spectroscopy (FTIR), thermo-gravimetric analyzer (TGA), thermo-mechanical analyzer, dynamic mechanical analyzer (DMA) and universal tensile machine (UTM). The moisture absorption, thermal and mechanical properties of polyimide films decreased with increasing the amount of 1,4-APB and HFBAPP. The polyimide films using HFBAPP showed lower properties than that of 1,4-APB at the same ratio, but it displayed better thermal properties and lower moisture absorption at the similar coefficient of thermal expansion (CTE) with a copper. On the basis of our finding, it is concluded that 4-component polyimide films could be utilized for base films for flexible copper clad laminates (FCCL) of flexible printed circuit boards.

• Polymer(Korea)
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• v.32 no.3
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• pp.230-238
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• 2008

The thermal and optical properties of cellobiose octa(cholestryloxycarbonyl)alkanoates CCCBn, $n=2{\sim}8$,10, the number of methylene units in the spacer) were investigated. All the samples formed monotropic cholesteric phases with left-handed helical structures. CCBn with n=2 or 10, in contrast with CCBn with $3{\leq}n{\leq}8$, did not display reflection colors over the full cholesteric range, suggesting that the helical twisting power of the cholesteryl group highly depends on the length of the spacer connecting the cholesteryl group to the cellobiose chain. The isotropic-cholestropic transition ($T_{ic}$) and glass transition temperatures decreased with increasing n and showed no odd-even effect. The transition entropy at $T_{ic}$ increased with increasing n from 2 up 6, but at n=7 it drops significantly and then increased again with increasing n from 8 to 10. The sharp change at n=7 may be attributed to a difference in arrangement of the side groups. The thermal stability and degree of order in the mesophase and the temperature dependence of the optical pitch observed for CCBn were significantly different from those reported for the cellulose tri(cholesteryloxycarbonyl)alkanoates and glucose penta(cholesteryloxycarbonyl)alkanoates. The results were discussed in terms of the differences in the degree of polymerization, the number of the mesogenic units per mole-glucose unit, and the conformation of the molecules.

• Korean Journal of Social Welfare Studies
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• no.37
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• pp.117-144
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• 2008

This is a timeseries study on the riving forces behind the changes of Korean welfare state. There are a few previous studies on the determinants of korean welfare state. These previous studies have some limitations in terms of reliability of the data source and validity of the statistical method used. Using the Comparative Social Policy Data-set(CSPD), we try to overcome the limitation of these previous studies. And adapting the time series regression, we examine the hypotheses about the changes of korean welfare state. In this study, four dependent variables are examined: the ratio of public social welfare expenditure to the GDP(WELGDP), the ratio of public social welfare expenditure to the government budget(WELGOV), the ratio of social expenditure to the GDP(SOCX), social welfare expenditure per capita. And independent variables were selected based on the theoretical background on the changes of welfare state. The results of this study as follows: First, the variables based on structural functionalism (industrialization) are the major driving forces behind the changes of korean welfare state since 1960s. Second, the effect of unemployment variable may be reasonably interpreted as reflecting the residual characteristics of korean welfare state. Third, the politics of the left based on power resource theory should be restrictedly interpreted. Ultimately, korean welfare state is still at rudimentary stage where the theory of industrialization is well applied as a driving forces behind the changes of welfare state.