• 한국농공학회논문집
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• 제52권1호
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• pp.51-59
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• 2010

The cemented sand and gravel (CSG) method is a construction technique that adds cement and water to rock-like materials, such as rivered gravel or excavation muck which that can be obtained easily at areas adjacent to dam sites. This study was performed to evaluate the unconfined compressive strength properties and freezing and thawing resistance of CSG materials with unit cement content. The three types of CSG-80, CSG-100 and CSG-120 with cement content were designed to evaluate the optimum water content, dry density, strength, stress-strain, micro structure and durability factor. As the results, the optimum water content ratio with cement content showed almost similar tendency, and the unconfined compressive strength and dry density increased as cement content increases. The strength ratio of 7 days for 28 days were in the range of 55~61 % and the strain ratio in stress-strain curve were in the range of 0.8~1.6 % nearby maximum strength in 28 days. It is expected that this study will contribute to increasing application of CSG method as well as to increasing the utilizing of CSG materials as a environmentally friendly CSG method.

• Macromolecular Research
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• 제16권4호
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• pp.329-336
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• 2008

Core/shell ($\pm$)PS/(-)silica nanocomposite particles were synthesized by dispersion polymerization using an amphoteric initiator, 2,2'-azobis [N-(2-carboxyethyl)-2,2-methylpropionamidine] ($HOOC(CH_2)_2HN$(HN=) $C(CH_3)_2CN$=NC $(CH_3)_2C$(=NH)NH $(CH_2)_2COOH$), VA-057. Negatively charged (-6.9 mV) silica was used as the stabilizer. The effects of silica addition time and silica and initiator concentrations were investigated in terms of polymerization kinetics, ultimate particle morphology, and size/size distribution. Uniform hybrid microspheres with a well-defined, core-shell structure were obtained at the following conditions: silica content = 10-15 wt% to styrene, VA-057 content=above 2 wt% to styrene and silica addition time=0 min after initiation. The delay in silica addition time retarded the polymerization kinetics and broadened the particle size distribution. The rate of polymerization was strongly affected by the silica content: it increased up to 15 wt% silica but then decreased with further increase in silica content. However, the particle size was only marginally influenced by the silica content. The zeta potential of the composite particles slightly decreased with increasing silica content. With increasing VA-057 concentration, the PS microspheres were entirely coated with silica sol above 1.0 wt% initiator.

• Journal of the Korean Wood Science and Technology
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• 제48권1호
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• pp.12-21
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• 2020

For quantitative evaluation of wooden structures, the mechanical performance of members has undergone outdoor exposure tests. A year-long monitoring was conducted using an SPF species. Test groups were divided into twelve (each month) to measure the moisture content, density and ultimate load. Starting from May when moisture content of the test group was at the lowest, simple failure modes were observed more frequently during the first half of the experiment, whereas complex failure modes took over during the second half. Starting from June when moisture content of the test group was the highest, ultimate load decreased by 30% in the second half compared to the first half. A multiple regression analysis confirmed that moisture content of the test group was the variable with most effect on ultimate load of various outdoor variables, and an estimation equation of a simple regression analysis revealed that moisture content and ultimate load formed an inversely proportionate relationship. It is thought that correlational relationships of variables other than moisture content could be applied with the increase in added data amount by longer periods of outdoor exposure tests.

• 한국인터넷방송통신학회논문지
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• 제24권1호
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• pp.43-48
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• 2024

본 연구는 최근 소비자의 경험을 자극하여 설득효과를 높이고 있는 모바일 어플리케이션의 효과를 살펴보고자 하였다. 특히 상업적 목적이 아닌, 공익적 목적의 콘텐츠들이 사용자의 태도와 신념에 어떠한 영향을 미치는지 확인하고자, 모바일 어플리케이션의 특성으로 상호작용성과 공익성을 선정하여 그 관계를 살펴보았다. 실제 어플리케이션 중 하나를 연구대상으로 선정하여 이를 체험한 피험자들의 반응을 조사하였다. 그 결과, 모바일 어플리케이션의 상호작용성과 공익성은 콘텐츠태도와 제품신념에 직·간접적인 영향력을 미치는 것으로 나타났으며, 콘텐츠태도가 신념에 영향을 줄 수 있음을 확인하였다. 이러한 연구결과는 수용자의 콘텐츠 태도를 강화함으로써 인식구조에 영향을 미칠 수 있음을 보여준다.

• Computers and Concrete
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• 제33권4호
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• pp.471-479
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• 2024

In urban areas, appropriate backfilling design is necessary to prevent surface subsidence and subsurface cavities after excavation. Expandable foam grout (EFG), a mixture of cement, water, and an admixture, can be used for cavity filling because of its high flowability and volume expansion. EFG volume expansion induces a porous structure that can be quantified by the entrapped air content. This study observed the unit weight variations in the EFG before and after expansion depending on the various admixture-cement and water-cement ratios. Subsequently, the air content before and after expansion and the gravimetric expansion ratios were estimated from the measured unit weights. The air content before expansion linearly increased with an increase in the admixture-cement ratio, resulting in a decrease in the unit weight. The air content after the expansion and the expansion ratio increased nonlinearly, and the curves stabilized at a relatively high admixture-cement ratio. In particular, a reduced water-cement ratio limits the air content generation and expansion ratio, primarily because of the short setting time, even at a high admixture-cement ratio. Based on the results, the relationship between the maximum expansion ratio of EFG and the mixture ingredients (water-cement and admixture-cement ratios) was introduced.

• 한국재료학회지
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• 제21권10호
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• pp.563-567
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• 2011

We report the structural characterization of $Bi_xZn_{1-x}O$ thin films grown on c-plane sapphire substrates by plasma-assisted molecular beam epitaxy. By increasing the Bi flux during the growth process, $Bi_xZn_{1-x}O$ thin films with various Bi contents (x = 0~13.17 atomic %) were prepared. X-ray diffraction (XRD) measurements revealed the formation of Bi-oxide phase in (Bi)ZnO after increasing the Bi content. However, it was impossible to determine whether the formed Bi-oxide phase was the monoclinic structure ${\alpha}-Bi_2O_3$ or the tetragonal structure ${\beta}-Bi_2O_3$ by means of XRD ${\theta}-2{\theta}$ measurements, as the observed diffraction peaks of the $2{\theta}$ value at ~28 were very close to reflection of the (012) plane for the monoclinic structure ${\alpha}-Bi_2O_3$ at 28.064 and the reflection of the (201) plane for the tetragonal structure ${\beta}-Bi_2O_3$ at 27.946. By means of transmission electron microscopy (TEM) using a diffraction pattern analysis and a high-resolution lattice image, it was finally determined as the monoclinic structure ${\alpha}-Bi_2O_3$ phase. To investigate the distribution of the Bi and Bi-oxide phases in BiZnO films, elemental mapping using energy dispersive spectroscopy equipped with TEM was performed. Considering both the XRD and the elemental mapping results, it was concluded that hexagonal-structure wurtzite $Bi_xZn_{1-x}O$ thin films were grown at a low Bi content (x = ~2.37 atomic %) without the formation of ${\alpha}-Bi_2O_3$. However, the increased Bi content (x = 4.63~13.17 atomic %) resulted in the formation of the ${\alpha}-Bi_2O_3$ phase in the wurtzite (Bi)ZnO matrix.

• 보존과학회지
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• 제17권
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• pp.57-64
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• 2005

청평사 강선루 회전문 부근에서 출토된 조선시대 $16\~17$세기 철물과 철촉에 대한 금속조직학적으로 조사하기 위하여 유물에서 부식되지 않은 시편을 채취하여 마운트와 연마 및 부식을 시켜 금속조직을 관찰하고 비금속개재물부분은 SEM으로 관찰한 뒤 EDS로 분석하였다. 금속학적 조직조사와 SEM-EDS분석을 통하여 철물과 철촉은 고체저온환원법에 의한 순철에 가까운 괴련철 혹은 해면철을 이용하여 철을 생산하고, 단야로 같은 곳에서 침탄을 하여 탄소량을 높인 것으로 밝혀졌다. 또한 철물은 탄소량을 어느 정도 높인 다음 담금질과 열처리과정을 반복하여 철기의 강도를 인위적으로 많이 높이는 작업을 한 것으로 밝혀졌다. 이번 조사연구를 통하여 조선시대에도 괴련철을 소재로 하여 철을 생산하였다는 것을 알 수 있어 의미 있는 결과를 얻었다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 추계 학술발표회 제20권2호
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• pp.769-772
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• 2008

공극은 열화인자의 이동경로가 되어 콘크리트의 성능을 저하시키는 요인으로 작용할 수 있으며 수분은 콘크리트 내부의 공극을 충전시킬 수 있기에 수분에 의한 투기성이 시멘트경화체의 공극구조에 미치는 영향을 평가하는 것은 중요하다. 이에, 본 연구에서는 공극구조와 투기성에 대하여 0%, 40%, 60%, 80%, 90%의 습도를 유지시킨 시험체와 화학조성물인 리튬실리케이트를 도포시켰을 경우의 공극구조 변화를 평가하였다. 그 결과, 함수율이 증가할수록 투기성은 저하되고 공극구조의 밀실성이 향상되어 수분에 의한 응축현상을 확인할 수 있었다. 그리고 수용액 상태의 리튬실리케이트는 수분을 함유하고 있는 상태에서 1$\mu$m 전, 후의 공극을 충전시켜 밀실성을 향상시키나함수조건에 따라 침투성에 의한 성능향상 범위가 제한적일 것으로 판단된다.

• 열처리공학회지
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• 제24권3호
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• pp.127-132
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• 2011

The silicon-containing Diamond-like Carbon (Si-DLC) film as an low friction coefficient coating has especially treated a different silicon content by plasma-enhanced chemical vapor deposition (PECVD) process at $500^{\circ}C$ on nitrided-STD 11 mold steel with (TMS) gas flow rate. The effects of variable silicon content on the Si-DLC films were tested with relative humidity of 5, 30 and 85% using a ball-on-disk tribometer. The wear-tested and original surface of Si-DLC films were analysed for an understanding of physical and chemical characterization, including a changing structure, via Raman spectra and nano hardness test. The results of Raman spectra have inferred a changing intra-structure from dangling bonds. And high silicon containing DLC films have shown increasing carbon peak ratio ($I_D/I_G$) values and G-peak values. In particular, the tribological tested surface of Si-DLC was shown the increasing hardness value in proportional to TMS gas flow rate. Therefore, at same time, the structure of the Si-DLC film was changed to a different intra-structure and increased hardness film with mechanical shear force and chemical reaction.

• Tribology and Lubricants
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• 제32권3호
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• pp.95-100
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• 2016

As an alternative fuel, biodiesel has excellent lubricating property. Previously, our research group reported that the properties of biodiesels depended on their composed molecular structure. In this study, we investigate lubricity and the mechanism of lubricity improvement of synthesized biodiesel molecules. We synthesize four types of biodiesel components from fatty acid via fisher esterification and soybean biodiesel from soybean oil via transesterification in high yield (92-96%). We analyze the lubricity of the five 5 types of biodiesel using HFRR (high frequency reciprocating rig). We estimate that the mechanism of lubricity is relevant to the molecular structure and structure conversion of biodiesel. The test results indicate that the longer the length of molecules and the higher the content of olefin, the better the lubricity of the biodiesel molecules. However, the wear scar size of the first test samples’ do not show a regular pattern with the wear scar size of the second test samples’. Moreover, we investigated the structure conversion of the biodiesels by using GC-MS for the recovered biodiesel samples from the HFRR test. However, we do not detect structure conversion. Thus, we conclude that the lubricity of biodiesel depends on how effectively solid adsorption and boundary lubrication occurs based on the size of the molecule and the content of olefin in the molecule. In addition, HFRR test condition in not sufficient for Diels-Alder cyclization of biodiesel components.