• 한국염색가공학회지
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• 제22권3호
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• pp.187-193
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• 2010

The effects of molecular weight (MW) and concentration on the rheological properties of poly(vinyl alcohol) (PVA) solutions in dimethyl sulfoxide (DMSO) were investigated at $30^{\circ}C$. Ubbelohde viscometer and rotational rheometer were employed for dilute and concentrated regime, respectively. In the dilute regime, the Mark-Houwink exponent ($\alpha$) of the solutions determined from three different MWs proved 0.73. The critical concentration (C*), in which the entanglement and overlap of polymer molecules began to take place, decreased with increasing the MW of PVA. Huggins constant ($K_H$) values ranged from 0.33 to 0.45 over the MW examined. In the log-log plot of $\eta_{sp}$ versus [$\eta$]C, the PVA with higher degree of polymerization (DP) gave a greater slope exhibiting the inflection point in the vicinity of C*. In the dynamic viscosity ($\eta'$) curve, the PVA solutions of DP 1700 presented Newtonian fluid behavior over most of the frequency range examined. However, the lower Newtonian flow region reduced with increasing the DP. As the PVA concentration increased, $\eta'$ was increased and the onset shear rate for pseudoplasticity was decreased. In the Cole-Cole plot, PVA solutions showed almost a single master curve in a slope of ca. 1.65 regardless of the DP. However, the increase of the concentration from 8 to 12 wt% for PVA solutions of DP 5000 decreased the slope from 1.73 to 1.57. In the tan $\delta$ curve, the onset frequency for sol-gel transition was shifted from 154 to 92 rad/s with increasing the DP from 3300 to 5000 and from 192 to 46 rad/s with increasing the concentration from 8 to 12 wt%. In addition, longer relaxation time ($\lambda$) was observed with increasing the DP and concentration.

• Tribology and Lubricants
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• 제30권2호
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• pp.108-115
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• 2014

The friction behaviors of bulk amorphous thermal spray coating (BAC) and second phase-reinforced composite coatings using a high velocity oxy-fuel spraying process were investigated using a ball-on-disk test rig that slides against a ceramic ball in an atmospheric environment. The surface temperatures were measured using an infrared thermometer installed 50 mm from the contact surface. The crystallinities of the coating layers were determined using X-ray diffraction. The morphologies of the coating layers and worn surfaces were observed using a scanning electron microscope and energy-dispersive spectroscopy. The results show that the friction behavior of the monolithic amorphous coating was sensitive to the testing conditions. Under lower than normal loads, a low and stable friction coefficient of about 0.1 was observed, whereas under a higher relative load, a high and unstable friction coefficient of greater than 0.3 was obtained with an instant temperature increase. For the composite coatings, a sudden increase in friction coefficient did not occur, i.e., the transition region did not exist and during the friction test, a gradual increase occurred only after a significant delay. The BAC morphology observations indicate that viscous plastic flow was generated with low loads, but severe surface damage (i.e., tearing) occurred at high loads. For composite coatings, a relatively smooth surface was observed on the worn surface for all applied loads.

• Geomechanics and Engineering
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• 제21권4호
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• pp.357-369
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• 2020

Different from the conventional planar fracture and simplified Newton model, for power-law slurries with a lower water-cement ratio commonly used in grouting engineering, flow model in geological rough fractures is built based on ten standard profiles from Barton (1977) in this study. The numerical algorithm is validated by experimental results. The flow mechanism, grout superiority, and water plugging of pseudo plastic slurry are revealed. The representations of hydraulic grouting properties for JRCs are obtained. The results show that effective plugging is based on the mechanical mechanisms of the fluctuant structural surface and higher viscosity at the middle of the fissure. The formulas of grouting parameters are always variable with the roughness and shear movement, which play a key role in grouting. The roughness can only be neglected after reaching a threshold. Grouting pressure increases with increasing roughness and has variable responses for different apertures within standard profiles. The whole process can be divided into three stationary zones and three transition zones, and there is a mutation region (10 < JRCs < 14) in smaller geological fractures. The fitting equations of different JRCs are obtained of power-law models satisfying the condition of -2 < coefficient < 0. The effects of small apertures and moderate to larger roughness (JRCs > 10.8) on the permeability of surfaces cannot be underestimated. The determination of grouting parameters depends on the slurry groutability in terms of its weakest link with discontinuous streamlines. For grouting water plugging, the water-cement ratio, grouting pressure and grouting additives should be determined by combining the flow conditions and the apparent widths of the main fracture and rough surface. This study provides a calculation method of grouting parameters for variable cement-based slurries. And the findings can help for better understanding of fluid flow and diffusion in geological fractures.

• Asian Pacific Journal of Cancer Prevention
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• 제15권13호
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• pp.5449-5454
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• 2014

Although genetic characteristics are considered to be a factor influencing the geographic variation in the prevalence of gallbladder cancer (GBC), they have not been well studied in Bolivia, which has a high prevalence rate of GBC. The purpose of this study was to examine the frequency of TP53 and K-ras mutations in Bolivian patients with GBC and to compare them with our previous data obtained in other high-GBC-prevalence countries, namely Japan, Chile, and Hungary. DNA was extracted from cancer sites in paraffin-embedded tissue from 36 patients using a microdissection technique. TP53 mutations at exons 5 to 8 and K-ras mutations at codons 12, 13 and 61 were examined using direct sequencing techniques. The data obtained were compared with those in the other high-GBC-prevalence countries. Of the 36 patients, 18 (50.0%) had a TP53 mutation (one mutation in each of 17 patients and three mutations in one patient), and only one (2.8%) had a K-ras mutation. Of the 20 TP53 mutations, 12 were of the transition type (60.0%). This rate was significantly lower than that in Chile (12/12, P<0.05). In addition, three mutations were of the CpG transition type (15.0%), which is a feature of endogenous mutation. All three were found in the hot spot region of the TP53 gene. In contrast, G:C to T:A transversion was found in Bolivia, suggesting the presence of exogenous carcinogens. Our findings suggest that the development of GBC in Bolivia is associated with both exogenous carcinogens and endogenous mechanisms. The identification of an environmental risk factor for GBC is needed to confirm these findings.

• 한국엔터테인먼트산업학회논문지
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• 제14권3호
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• pp.117-132
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• 2020

본 연구의 목적은 한국과 독일의 평생교육정책을 역사적 변천과정을 중심으로 검토하여 이를 토대로 한국의 평생교육정책에 바람직한 발전방안을 모색하는데 있다. 이를 위해 한국과 독일의 평생교육에 대한 연구논문과 독일 연방 교육연구부(BMBF), 독일 성인교육연구소(DIE), 독일 성인교육협회(DVV), 유럽 성인교육협회(EAEA), 유네스코 평생학습연구소(UIL)와 국가평생교육진흥원에서 발간한 실무자료 등을 활용하여 한국과 독일의 평생교육정책을 비교·분석하였다. 연구결과, 독일의 평생교육정책은 지역의 특성에 맞는 프로그램을 운영하는 가운데, 사회적·직업적 전문성 향상을 촉진하고 있으며, 한국의 평생교육정책은 정치적 민감성 때문에 시민교육이 지자체 단위의 평생교육 차원에서 미비한 수준임을 확인할 수 있었다. 또한, 독일의 경우 평생교육 참여가 용이한 환경에 대한 구축을 통하여 평생교육 참여율에 대한 확대를 추진하고 있으며, 이에 반해 한국의 평생교육 참여율은 경제협력개발기구(OECD)선진국에 비해 낮은 상태인 것으로 확인되었다. 마지막으로, 독일의 평생교육정책은 교육에 있어서 독립이라는 이념적 원칙에 따라 사회의 요구에 자연스러운 변화를 추구하고 있으며, 그에 반해 한국의 평생교육정책은 중앙정부에 의해 통제되는 경향이 강한 것을 확인할 수 있었다. 본 연구결과 독일의 평생교육정책은 한국의 평생교육정책에 다음과 같은 시사점을 제공한다. 첫째, 학습자의 교육 수요가 다양해짐에 따라 공급자 중심에서 학습자 중심 교육체계에 대한 확대이다. 둘째, 직업분야의 평생교육에 대한 활성화이다. 셋째, 양질의 평생학습 지원을 위한 평생교육 예산 확대이다. 넷째, 지속가능한 평생학습사회 실현을 위한 종합적이고 장기적인 시스템 구축이 이루어져야 한다.

• 대한바이러스학회지
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• 제26권1호
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• pp.9-22
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• 1996

Respiratory Syncytial virus (RSV) is an important cause of acute lower respiratory tract infections in human, with infants and young children being particularly susceptible. In the temperate zones, sharp annual outbreaks of RSV occur during the colder months, in both the northern and the southern hemisphere. RSV is unusual in that it can repeatedly reinfect individuals throughout life and infect babies in the presence of maternal antibody. RSV isolates can be divided into two subgroups, A and B, on the basis of their reactions with monoclonal antibodies, and the two subgroups are also distinct at the nucleotide sequence level. The specific diagnosis of RSV infection was best made by isolation of virus in tissue culture, identification of viral antigen, or by specific serologic procedures. Recently, rapid detection of RSV and analysis of RSV strain variation became possible by development of methods of reverse transcription and polymerase chain reaction amplification. In this study, to determine the genetic diversity of RSV found in Korea, 173 bp and 164 bp spanning selected regions of the RSV F and SH genes were enzymatically amplified and sequenced, respectively. Eight for F gene and three for SH gene were detected in 66 nasopharyngeal swap samples tested. Two major antigenic subgroups, A and B were confirmed from Korean samples (seven for subgroup A and one for subgroup B). At the nucleotide level of the F gene region, Korean subgroup A strains showed 95-99% homologies compared to the prototype A2 strain of subgroup A and 93-100% homologies among Korean subgroup A themselves. For the SH gene region, Korean subgroup A strain showed 97.5% homology compared to the prototype A2 strain of subgroup A, and Korean subgroup B strain showed 97% homology compared to the prototype 18537 strain of subgroup B. Most of base changes were transition and occured in codon position 3, which resulted in amino acid conservation. Using the maximum parsimony method, phylogenetic analysis indicated that Korean RSV strains formed a group with other RSV strains isolated from the United States, Canada, the Great Britain and Australia.

• 한국재료학회지
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• 제17권8호
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• pp.414-419
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• 2007

We report the electrical conductivity of the mixed alkali silicate glasses in the system (60-x)$SiO_2-40Na_2O-xCaO(x=0\sim15wt%)$ in the temperature range from $150^{\circ}C$ to $620^{\circ}C$. In the range from $150^{\circ}C$ to glass transition temperature$(T_g)$, the electrical conductivities of glass samples had a tendency to be proportion with temperature. The glasses of containing over 7.5wt% CaO showed lower conductivities than the glasses of containing 0 and 5wt% CaO because two kinds of alkali ions$(Na^+,\;Ca^{2+})$ were obstructed each other. On the other hand, in the range from $T_g$ to $620^{\circ}C$, the electrical conductivity of glasses($7.5{\leq}x{\leq}12.5$) was unstable and decreased in some region. From XRD results, the $Na_4Ca(SiO_3)_3$ phase were observed in these glasses. This means the alkali ions didn't behave as carrier, it seems that this caused the conductivities decrease. In case of glass of containing 15wt% CaO, any crystal phase were not observed. This means the alkali ions behaved as carrier, it consequently seems the conductivity increased.

• Journal of Pharmaceutical Investigation
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• 제29권3호
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• pp.193-203
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• 1999

In order to investigate systematically the steady shear flow properties of aqueous po1y(ethylene oxide) (PEO) solutions having various molecular weights and concentrations, the steady flow viscosity has been measured with a Rheometrics Fluids Spectrometer (RFS II) over a wide range of shear rates. The effects of shear rate, concentration, and molecular weight on the steady shear flow properties were reported in detail from the experimentally measured data, and then the results were interpreted using the concept of a material characteristic time. In addition, some flow models describing the non-Newtonian behavior (shear-thinning characteristics) of polymeric liquids were employed to make a quantitative evaluation of the steady flow behavior, and the applicability of these models was examined by calculating the various material parameters. Main results obtained from this study can be summarized as follows: (1) At low shear rates, aqueous PEO solutions show a Newtonian viscous behavior which is independent of shear rate. At shear rate region higher than a critical shear rate, however, they exhibit a shear-thinning behavior, demonstrating a decrease in steady flow viscosity with increasing shear rate. (2) As an increase in concentration and/or molecular weight, the zero-shear viscosity is increased while the Newtonian viscous region becomes narrower. Moreover, the critical shear rate at which the transition from the Newtonian to shear-thinning behavior occurs is decreased, and the shear-thinning nature becomes more remarkable. (3) Aqueous PEO solutions show a Newtonian viscous behavior at shear rate range lower than the inverse value of a characteristic time $1/{\lambda}_E$, while they exhibit a shear-thinning behavior at shear rate range higher than $1/{\lambda}_E$. For aqueous PEO solutions having a broad molecular weight distribution, the inverse value of a characteristic time is not quantitatively equivalent to the critical shear rate, but the power-law relationship holds between the two quantities. (4) The Cross, Carreau, and Carreau-Yasuda models are all applicable to describe the steady flow behavior of aqueous PEO solutions. Among these models, the Carreau-Yasuda model has the best validity.

• 한국환경생태학회지
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• 제33권5호
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• pp.552-564
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• 2019

본 연구는 낙엽활엽수와 상록활엽수가 혼효하는 곳으로 식물학적 가치가 높은 두륜산도립공원 일대의 상록활엽수림을 대상으로 식생 특성을 파악하고자 진행하였다. 식생 특성을 알아보기 위해 $100m^2$ 크기의 조사구 40개소를 설치하여 조사 분석하였다. 두륜산도립공원이 위치한 해남군은 난대림지역으로 40년간의 기상자료를 분석한 결과, 한랭지수 $-8^{\circ}C$ 월, 온량지수 $109.2^{\circ}C$ 월, 연평균강수량 1,310.5mm로 상록활엽수림의 분포적지라 할 수 있다. TWINSPAN에 의한 군락분류 결과, 붉가시나무군락-I, 붉가시나무군락-II, 참식나무-푸조나무군락 총3개 군락으로 분리되었다. 두륜산도립공원 내 상록활엽수림은 교목층에 우점하고 있는 붉가시나무가 아교목층에서도 세력을 넓혀가고 있으며, 붉가시나무 외에 교목성상의 상록활엽수인 참식나무와 생달나무 등이 전 층위에서 확인되고 있는 형태로 굴참나무, 졸참나무, 개서어나무 등의 낙엽활엽수가 도태되고 상록활엽수인 붉가시나무군락으로의 천이가 진행되고 있으며, 국지적으로 참식나무군락이 출현하고 있었다. 종다양도는 붉가시나무군락-I(1.3208), 붉가시나무군락-II(1.4916)에 비해 참식나무-푸조나무군락(1.0798)이 낮게 나타났다.

• 박물관보존과학
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• 제28권
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• pp.17-34
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• 2022

이 연구에서는 송파 지역의 석촌동고분군 연접적석총과 방이동고분군 3호분에서 출토된 토기를 대상으로 재질특성을 파악하고 출토지에 따른 재료의 동질성과 소성온도를 해석하였다. 유적들은 비교적 근래에 연구가 이루어진 곳으로, 이를 포함하고 있는 고분군은 고대 한반도 묘제의 변천과정을 보여주며 동시에 당시 중앙세력에 대한 중요한 고고자료를 제공하고 있다. 두 유적에서 출토된 연구대상 토기는 각기 다른 시기에 매장되었으나, 호정 및 불호정성을 띠는 원소들의 거동양상과 주구성성분을 통해 살펴본 풍화경향으로 보아 유사한 편마암류의 풍화토를 수급하여 제작한 것으로 여겨진다. 또한 광물조성과 태토의 미세조직을 살펴본 결과, 상대적으로 이른 시기인 석촌동 토기들은 950℃ 이하에서 소성된 것으로 판단된다. 반면 방이동 3호분 토기는 850℃ 이하와 1,000℃ 이상의 온도를 경험한 것으로 확인되어 차이를 보인다. 그러나 시기에 따른 소성온도의 고온화로 해석하기에는 어려움이 있으며, 향후 보다 다양한 토기 및 고토양과의 비교를 통해 토기의 제작기술 변화를 해석할 수 있을 것으로 기대된다.