• 한국태양에너지학회:학술대회논문집
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• 한국태양에너지학회 2012년도 춘계학술발표대회 논문집
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• pp.194-199
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• 2012

In this study, for increasing the efficiency of solar collector, the thermal conductivities and viscosities of the pure water and ethanol oxidized multi-walled carbon nanofluids were measured. Nanofluids were manufactured by ultra-sonic dispersing oxidized multi-walled carbon nanotubes(OMWCNTs) in the pure-water and ethanol at the rates of 0.0005 ~ 0.1 vol%. the Thermal conductivities and viscosities of manufactured nanofluids were measured at the low temperature($10^{\circ}C$), the room temperature($25^{\circ}C$) and the high temperature($70^{\circ}C$). For measuring thermal conductivity and viscosity, we used Transient Hot-wire Method and Rotational Digital Viscometer, respectively. As a result, under given temperature conditions, thermal conductivity of the 0.1 vol% pure-water nanofluid improved 7.98% ($10^{\circ}C$), 8.34% ($25^{\circ}C$), and 9.14% ($70^{\circ}C$), and its viscosity increased by 37.08% ($10^{\circ}C$), 33.96% ($25^{\circ}C$) and 21.64% ($70^{\circ}C$) than the base fluids. Thermal conductivity of the 0.1 vol% ethanol nanofluids improved 33.72% ($10^{\circ}C$), 33.14% ($25^{\circ}C$), and 32.36% ($70^{\circ}C$), and its viscosity increased by 37.93% ($10^{\circ}C$), 31.92% ($25^{\circ}C$) and 29.42% ($70^{\circ}C$) than the base fluids.

• 한국세라믹학회지
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• 제34권1호
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• pp.70-78
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• 1997

3Y TZP/SUS316계 경사기능재료를 슬립캐스팅법을 이용하여 제조하였다. 슬립캐스팅 공정에서 석고몰드를 대체하기 위해 알루미나몰드를 제조하였고, 3Y-TZP/SUS316 2상 슬러리의 최적 분산조건을 ESA, 점도계, 침전거동의 관찰 등을 통해 결정하였으며, 석고몰드와 알루미나몰드로 캐스팅한 시험편의 제반 특성을 소결수축율변화, 건조 및 소결거동, 미세구조 관찰 등으로 조사하였다. 그 결과 알루미나몰드를 사용하여 제조된 시험편에서는 석고몰드 사용시 나타나는 표면에서의 오염이 관찰되지 않았으며, 각 층의 두께조절이 쉬웠고 높은 재현성을 나타냄을 알 수 있었다. 특히 알루미나몰드를 사용하여 제조한 SUS316에서는 어떤 열화현상도 관찰되지 않았다. 결국 슬립캐스팅 공정으로 3Y-TZP/SUS316계 경사기능재료를 제조함에 있어서 기존의 석고몰드보다 다공질 알루미나몰드의 사용이 바람직하다는 것을 알 수 있었다.

• Maxillofacial Plastic and Reconstructive Surgery
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• 제27권5호
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• pp.424-430
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• 2005

The oral cavity is humid environment mainly due to the continuous salivary flow. The reaction of oral mucosa to fluid flow is important for homeostasis and pathogenesis. The objective of this study is the screening the change of gene expression after the application of fluid induced shear stress (FISS) on the gingival fibroblast using cDNA microarray assay. The immortalized human gingival fibroblasts were grown and FISS was applied using a cone viscometer at a rotational velocity of 40 rpm, respectively for periods of 2 and 4 hours. The synthesis of cDNA was done from the extracted total RNA and cDNA microarray assay was done subsequently. The genes that showed over 1.6 in the Cy3/Cy5 or the Cy5/Cy3 value were regarded as genes influenced significantly by the FISS application ion (/M/>0.7). The " RUNX-1" was increased its expression in 2 hours group and " RUN and SH3 domain containing 1" was increased its expression in 4 hours group. The "CC020415", "cyclin L1", "interferon regulatory factor1", "early growth response 1", "immediate early response 2", and "immediate early response 3" genes were increased their expression in 2 and 4 hours after FISS application. In conclusion, we could find many genes that were probably related to the FISS application. Interestingly, most of them were placed in similar molecular pathways and these findings improve the reliability of chip data and usefulness in overall screening. From this experiment, we could find many items for further study and it will make improvement in the understanding of intracellular events in response to FISS.

• Journal of Oral Medicine and Pain
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• 제39권3호
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• pp.90-95
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• 2014

Purpose: To investigate viscosity and wettability of hyaluronic acid (HA) solutions according to supplementation of lysozyme and/or peroxidase, and different ionic strength and pH conditions. Methods: Solutions containing HA were prepared using distilled deionized water (DDW) and simulated salivary buffer (SSB) in different conditions. Different concentrations of hen egg-white lysozyme and bovine lactoperoxidase was added into HA solutions. HA solutions with antimicrobials in different ionic strength and pH conditions were prepared. Viscosity was measured using cone-and-plate digital viscometer at six different shear rates and wettability on acrylic resin and Co-Cr alloy was determined by contact angle. Results: The viscosity values of HA dissolved in DDW were decreased in order of HA, HA containing lysozyme, HA containing peroxidase, and HA containing lysozyme and peroxidase. The viscosity values for HA in DDW were decreased as the concentration of lysozyme and/or peroxidase increased. However, the viscosity values for HA in SSB showed no significant changes according to the concentration of lysozyme and/or peroxidase. The viscosity values of HA solutions were inversely proportional to ionic strength and pH. The contact angle of HA solutions showed no significant differences according to tested surface materials, addition of lysozyme and/or peroxidase, and different ionic strength and pH conditions. Contact angles on acrylic resin by HA solutions in all tested conditions were much higher than those by human saliva. Conclusions: The rheological properties of HA supplemented with lysozyme and/or peroxidase in different ionic strength and pH conditions were objectively confirmed, indicating the possibility of HA with lysozyme and/or peroxidase as main components in the development of effective saliva substitutes.

• 한국산학기술학회논문지
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• 제15권3호
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• pp.1247-1252
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• 2014

본 연구에서는 온도조건에 따른 MR 유체의 물리적 특성을 연구하고자 침전 및 전단응력실험을 수행하였다. MR 댐퍼에 사용되는 MR 유체는 자성 파우더를 포함하고 있어 침전현상이 발생하므로 침강성과 인가전류에 의한 전단응력 변화를 상온과 고온조건에서 실험하였다. 침강특성을 조사하기 위하여 강제 대류형 오븐을 인가전류에 의한 전단응력을 측정하기 위하여 점도계를 사용하였다. 실험결과로부터 MR 유체는 시간과 온도에 따른 침강 특성이 다름을 그리고 교반시간이 큰 경우에 MR 유체의 분산성이 2배 이상 우수하였다. 전단률이 증가할수록 전단응력은 로그함수의 증가분포를 인가전류를 증가할수록 2차 함수의 증가분포를 그리고 MR 유체의 전단응력은 상온보다 고온에서 6-18% 낮은 분포를 보였다.

• 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.

• 한국식품과학회지
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• 제16권4호
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• pp.451-456
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• 1984

$6{\sim}10%$ 쌀전분의 가열 및 알카리호화액에 대하여 시간의존성 리올로지특성을 회전점도계를 사용하여 검토하였다. 시료 모두 항복응력을 갖는 틱소트로픽유체로 거동하였으나 알카리호화액의 시간의존성이 더 컸으며 전단에 대한 안정성을 보였다. 시간의존특성은 전단 시간 20분까지 Tiu들의 유동모형식에 잘 적용되었으며 식에 포함된 구조의 파괴속도상수 $a_1$ 값은 호화액의 구조적상태변화와 밀접한 상관성을 갖는 것으로 나타났다. $a_1$ 값은 전단속도에 대하여는 두시료에서 모두 직선적인 증가경향을 보였으며 농도 및 온도에 대하여는 겉보기 점도와 마찬가지로 지수적인 관계를 나타내었다. 8 % 쌀전분의 가열호화액에 대한 $a_1$ 의 온도의존성은 겉보기점도보다 더 큰 것으로 나타났으며 $30{\sim}70^{\circ}C$에서 측정한 $a_1$ 및 겉보기 점도의 활성화에너지는 각각 6.8 및 14.3 $kcal/g{\cdot}mol$ 이었다.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2003년도 학술대회지
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• pp.229-234
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• 2003

As electrorheological fluid(ER fluid) has a characteristic that apparent viscosity varies when electric field applied, so rheological characteristic(yield stress & viscosity) changes in proportion to the electric field applied and the response time is very short within a few miliseconds . In case of using ER fluid for journal bearing as lubricant, it is estimated that it's possible to realize very effective journal bearing system that is not complicate and has a very quick response time. It is necessary to examine the influence of rheological characteristic that varies with electric field applied on bearing characteristic to apply ER fluid to journal bearing, however there are few studies for about that. As for the journal bearing, it comes under high shear flow mode that has shear rate range of $10^3\~10^4s^{-1}$ because rotational speed is very high and clearance is small. But most of the studies for about ER fluid issued until now is about the range of $10\~10^2s^{-1}$. So, there are a lot of difficulties to understand the characteristic offish shear flow mode and furthermore it is restricted to make an experiment for about the characteristic of ER fluid because of the limitation of experimental equipment. The equipment was prepared to make an experiment lot high shear flow mode that has the range of $10^3\~10^4s^{-1}$ using ER fluid that is composed of silicon oil with dispersed particle of starch. Using the above system, the fluid characteristic of ER fluid was studied.

• Applied Biological Chemistry
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• 제34권4호
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• pp.360-365
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• 1991

신선찰벼(일반계)와 한강찰벼(다수계) 전분의 특성을 이해하기 위하여 $4{\sim}8%$ 전분 현탁액의 가열 및 알칼리 호화에 의한 리올로지 특성을 회전점도계로 비교 검토하였다. 한강찰벼 전분의 전단응력 값이 가열 및 알칼리 호화액에서 모두 컸으며, 시료간의 차이는 알칼리 호화액에서 더 컸다. 가열 및 알칼리 호화액에서 점조도지수 및 항복응력값은 한강찰벼 전분이 컸으며, 시료간의 차이는 알칼리 호화액에서 더 컸다. 또 가열 호화액보다 알칼리 호화액이 항복응력의 농도의존성과 항복응력을 나타내기 시작하는 농도가 높았다.

• 한국식품과학회지
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• 제35권1호
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• pp.155-158
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• 2003

겨자 페이스트의 시간의존성을 관찰하기 위해 총고형분 함량(18, 21, 24, 27, 30%)과 전단속도$(15,\;20,\;25\;s^{-1})$를 달리하여 시간-전단응력 변화가 분석되었으며, 이들 데이터들은 Figoni 및 Shoemaker 모델, Weltman 모델, Hahn 모델에 적용하여 정량적으로 평가되었다. 일정한 전단속도에서 겨자페이스트의 농도가 증가함에 따라 보다 높은 전단응력을 나타냈으며, 3종류의 모델식에서의 각 매개변수들은 농도에 따라 일정한 경향을 나타내어 겨자 페이스트의 시간의존 유동 특성에는 다른 분산식품들과 마찬가지로 농도에 의해 크게 영향을 받음을 알 수 있었다. 그러나 일정 농도를 기준으로 전단속도에 따른 시간의존성 변화에서는 25%와 27%농도를 가진 시료를 제외하고는 각 매개변수 값들의 차이는 거의 없는 것으로 나타났다. 시간의존 유동특성 모델에 적용한 결과, Weltman 모델이 다른 모델식에 비해 가장 높은 결정계수$(R^2)$을 보여주고 있어 Weltman 모델식이 겨자 페이스트 시간의존성을 나타내는 가장 적합한 모델식임을 알 수 있었다.