• 산업기술연구
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• 제24권A호
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• pp.165-171
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• 2004

Latex modification of concrete provides the material with higher flexural strength, as well as high bond strength and reduced water permeability. However, If the thermal expansion properties of overlay concrete (latex-modified concretes) are big different from that of substrate (ordinary portland cement concrete), these would cause a big interfacial stresses and result in premature failure. Therefore, the purposes of this study were to investigate thermal expansion characteristics of latex-modified concrete with cement types. The result of thermal expansion showed the coefficient of thermal expansion of concretes increased with latex inclusion. The coefficient of thermal expansion of RSLMC was a little smaller than that of LMC, which might be due to the finer cement grain, compacter internal, and stiffer properties of concrete. However, the coefficients of LMC and RSLMC were quite similar to that of ordinary cement concrete. Thus, this would not cause an interfacial stresses and will enable to ensure long-term performance of concrete bridge deck overlays.

• Journal of the Korean Wood Science and Technology
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• 제27권4호
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• pp.57-64
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• 1999

This research was carried out to investigate the effects of density, resin and particle types on the physical and mechanical properties of the composites made from various wood particles mixed with coating paper. The experiment was designed to apply with three particles (flake, chip, and fiber) and three resin types (urea, phenol and PMDI resin). The mixed ratio of coating paper to wood particle was fixed on 50 to 50% in each board making. And also it was designed to apply for four density levels (0.6, 0.7, 0.8 and 0.9 g/$cm^3$) and four mixed formulations of coating paper to wood particle (10:90, 20:80, 30:70, and 40:60 %) to analyze clearly the effects of PMDI resin. Coating paper-wood particle composites have acceptable bending strength (MOR, MOE) though the mixed ratio of coating paper was increased, but have low internal bond strength and poor dimensional stability (WA, TS, LE). Composites with high density had higher mechanical properties but showed lower physical properties than composites with low density. In conclusion, at least up to 20% mixed ratios, coating paper-wood particle composites have acceptable physical and mechanical properties, and PMDI resin has possibility for coating paper-wood particle composite manufacture.

• 한국미생물·생명공학회지
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• 제32권4호
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• pp.347-351
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• 2004

Hydrolysis of manno-oligosaccharides and galactomannan was studied with the purified Bacillus subtilis WL-7 mannanase from recombinant Eschericoli. The predominant products of hydrolysis were mannose, mannobiose and mannotriose. The enzyme could hydrolyze $\beta$-1 A-linked manno-oligosaccharides larger than mannobiose, but was not active on mannobiose. When the mannanase hydrolyzed manno-oligo saccharides of degree of polymerization(DP) 4-6, it was more active on the substrate of higher DP. Based on analysis of transient reaction products by TLC, the enzyme was found to have a preference for internal $\beta$-IA-mannosidic linkages, which are the central mannosidic bond of mannotetraose and the two middle mannosidic bonds of mannopentaose. The $\beta$-l A-mannosidic bonds situated at the second and fourth positions from the nonreducing end of mannohexaose were preferenhydrolyzed by the mannanase. Locust bean gum(LBG) was enzymatically hydrolyzed with higher efficiency than guar gum, resulting that amount of reducing sugars was liberated more efficiently from LBG than guar gum with same activity of mannanase.

• Journal of the Korean Wood Science and Technology
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• 제29권3호
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• pp.27-35
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• 2001

Four different sources of wood-fibers from Eucalyptus, Italian poplar, hemlock, and mixed species fibers were used to study the influence of their fiber characteristics on the performance of medium density fiberboard (MDF) panels bonded with both urea-formaldehyde (UF) and phenol-formaldehyde (PF) adhesives. Included fiber characteristics were fiber length, size distribution, bulk density, and acidity. Physical and mechanical properties of MDF panels manufactured by dry process using these different fibers were determined for the comparison of board performance. Two hardwood species had a large fraction of short fibers resulting in a higher bulk density while very long hemlock fibers had lower bulk density. Fiber acidity was revealed to strongly affect the internal bond (IB) strength of MDF panels bonded with UF resins. MDF panels made from mixed species fibers showed highest IB strength of all panels prepared. UF-bonded MDF panels showed poor dimensional stability. In conclusion, the present study showed that wood-fiber characteristics such as fiber length, bulk density, and acidity affect the performance of MDF boards, and also suggested that fiber characteristics be considered for MDF panel manufacture.

• Structural Engineering and Mechanics
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• 제53권6호
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• pp.1083-1104
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• 2015

This paper provides the results of an experimental investigation into the flexural behavior of continuous two-span unbonded post-tensioned high strength concrete (HSC) beams, strengthened by end-anchored CFRP laminates of different configurations in the hogging region. Implementing two different configurations of end-anchorage systems consisting of steel plates and bolts and carefully monitoring the development of strains throughout the load history using sufficiently large number of strain gauges, the response of beams including the observed crack propagations, beam deflection, modes of failure, capacity enhancement at service and ultimate and the amount of moment redistribution are measured, presented and discussed. The study is appropriate in the sense that it covers the more commonly occurring two span beams instead of the simply supported beams investigated by others. The experiments reconfirmed the finding of others that proper installation of composite strengthening system is most important in the quality of the bond which is essential for the internal transfer of forces. It was also found that for the tested two span continuous beams, the capacity enhancement is more pronounced at the serviceability level than the ultimate. This is an important finding as the design of these beams is mostly governed by the serviceability limit state signifying the appropriateness of the suggested strengthening method. The paper provides quantitative data on the amount of this capacity enhancement.

• 한국화재소방학회논문지
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• 제32권1호
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• pp.116-121
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• 2018

본 연구는 소방공무원의 임파워먼트와 가족기능 수준이 우울에 미치는 영향을 알아봄으로써 소방공무원의 우울에 관한 예방 차원의 실천 방안을 마련하는데 도움을 주고자 하였다. 이를 위하여 경기지역 소방공무원 351명을 대상으로 유의표집 방식으로 조사하였다. 조사결과, 소방공무원의 우울에 임파워먼트와 가족기능이 모두 유의미한 영향을 미치는 것으로 나타났다. 본 연구결과를 토대로, 소방공무원의 정신건강 예방을 위해 내적 대처자원으로서 각 개인의 임파워먼트를 적용해 볼 수 있는 가능성을 보여주었다는 점과 소방공무원 가정의 가족기능을 강화하기 위한 다양한 대안이 필요하며, 가족의 건강성 회복을 이끌어내기 위해 예방차원의 효과적인 '일과 삶의 균형' 정책의 적극적 도입과 지원을 제안하였다.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2001년도 추계학술발표회 초록집
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• pp.56-56
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• 2001

Ni-W alloy deposit is one of the best alternatives to hard chromium plating because of its good mechanical properties (high hardness, high strength, and good wear resistance). Ni-W alloy is deposited from weakly acidic or alkaline electrolytic bath with nickel sulfate, sodium tungstate or APT, and some kinds of organic hydroxy-acid complex and ammonia salts. W content of the deposit can be changed from 0 to 5Owt% and the coating with high W content is more attracted. But, meanwhile, the deposited layers are always found high internal stress, which cause them to become brittle and to bond insufficiently with the substrate. On the second hand, as the W content is incresed, the current efficiency reduced, which results in large quantities of hydrogen evolution and then produces bubbles on surface and pitting appearance In this paper, the influence of some additives on Ni-W alloy electroplating was investigated by means of compositional analysis and SEM. The initial results showed that 2-butyne-1,4-diol was the best brightener for Ni-W plating process. It could brighten and level deposit, but decreased the cathodic current efficiency. Its optimum concentration range is from O.lgjL to 0.5gjL. Besides, three kinds of additives including 2-butyne-1,4-diol were examined with Dagguchi method.

• 한국가구학회지
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• 제18권3호
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• pp.205-210
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• 2007

Particleboard(PB) is one of the most commonly used wood-based composite materials, which can be prepared by utilizing any kind of low grade wooden materials like waste wood which contains formaldehyde itself. Therefore, PB have been of considerable interest, in issues regarding the formaldehyde emission problems. Wood wastes are carbonized by the carbonization kiln at $800^{\circ}C$. Charcoal has been known as a formaldehyde adsorber. Thus, in this study, we fabricated PBs with carbonized waste particles cores, to examine the possibility of developing less formaldehyde emitting boards. The physical and mechanical properties were evaluated by Korean Standard (KS F 3104). The moisture content of PBs ranged from 6.76 to 8.36%. Internal bond strengths decreased with the increase in the content of carbonized core particles. Formaldehyde emission showed minimum value at 25% of carbonized core particles, but the emission values increased when the amount of carbonized cote particles increased. When 25% of carbonized core particles was used, PBs met KS F 3104 standard properties.

• Journal of the Korean Wood Science and Technology
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• 제41권6호
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• pp.544-550
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• 2013

국내에서 생산된 파티클보드에 대한 나사못 유지력을 기존의 식으로부터 수정 보완된 예측 식으로 나타내기 위해 나사못 유지력실험을 실시했다. 본 연구에 사용된 나사못은 No. 6, No. 8 및 No. 10이었다. 나사못 유지력의 예측 식은 나사못의 직경과 관입길이, 파티클보드의 비중 및 IB의 함수로 나타냈다. 예측 식은 길이가 서로 다른 No. 8 나사못의 실험결과와 상당히 일치하였다. 파티클보드에 대한 실험결과들과 표면에서 나사못 유지력의 예측 값은 비중보다 IB가 더 좋은 예측인자였고, 측면에서는 IB보다 비중이 더 일치하였다.

• Computers and Concrete
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• 제18권2호
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• pp.267-278
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• 2016

In order to observe the internal damage of concrete in real time, we introduced acoustic emission nondestructive detecting technology into a series of fracture tests; the test results revealed the whole process that concrete undergoes when it sustains damage that leads to failure, according to the change rules of the acoustic emission parameters. The results showed that both the initiation and unstable loads can be accurately determined using the abrupt change of the acoustic emission rate curves and the turning point of the acoustic emission parameters' accumulative curves. The whole process, from damage to failure, includes five phases, beginning with damage, such as cracking, a stable crack growth process, a critical unstable stage, and unstable propagation. The brittle fracture characteristics of concrete change when steel bars are joined, because the steel bars and the concrete structure bond, which causes an increase in the acoustic emission signals within the fracture process of the reinforced concrete. The unstable propagation stage is also extended. Our research results provide a valid methodology and technical explanations, which can help researchers to monitor the cracking process of concrete structures, in real time, during actual projects.