• Bulletin of the Korean Chemical Society
• /
• 제28권8호
• /
• pp.1425-1428
• /
• 2007

• Korea-Australia Rheology Journal
• /
• 제14권4호
• /
• pp.189-201
• /
• 2002

The interaction between hydrophobically modified hydroxyethyl cellulose (hmHEC), containing approximately 1 wt% side-alkyl chains of $C_{16}$, and an anionic sodium dodecyl sulphate (SDS) surfactant was investigated. For a semi-dilute solution of 0.5 wt% hmHEC, the previously observed behaviour of a maximum in solution viscosity at intermediate SDS concentrations, followed by a drop at higher SDS concentrations, until above the cmc of surfactant when the solution resembles that of the unsubstituted polymer, was confirmed. Additionally, a two-phase region containing a hydrogel phase and a water-like supernatant was found at low SDS concentrations up to 0.2 wt%, a concentration which is akin to the critical association concentration, cac, of SDS in the presence of hmHEC. Above this concentration, SDS molecules bind strongly to form mixed micellar aggregates with the polymer alkyl side-chains, thus strengthening the network junctions, resulting in the observed increase in viscosity and elastic modulus of the solution. The shear behaviour of this polymer-surfactant complex during steady and step stress experiments was examined In great detail. Between SDS concentrations of 0.2 and 0.25 wt%, the shear viscosity of the hmHEC-polymer complex network undergoes shear-induced thickening, followed by a two-stage shear-induced fracture or break-up of the network. The thickening is thought to be due to structural rearrangement, causing the network of flexible polymers to expand, enabling some polymer hydrophobic groups to be converted from intra- to inter-chain associations. At higher applied stress, a partial local break-up of the network occurs, while at even higher stress, above the critical or network yield stress, a complete fracture of the network into small microgel-like units, Is believed to occur. This second network rupture is progressive with time of shear and no steady state in viscosity was observed even after 300 s. The structure which was reformed after the cessation of shear is found to be significantly different from the original state.

• Asian-Australasian Journal of Animal Sciences
• /
• 제12권3호
• /
• pp.422-428
• /
• 1999

The mineral status of native goats and forage species, namely; Cynodon plectostachyus, Pennisetum purpureum. Eleusine indica, Cynodon dactylon, Calopogonium muconoides, Centrosema pubescens, Leucaena leococephala, and Mimosa pudica in lahar affected areas of Concepcion, Tarlac, Philippines were determined. Forage and blood samples were collected six times in 1996-97, and analyzed for calcium, phosphorus, magnesium, sulfur, copper, iron, molybdenum, selenium, and zinc. Forage calcium and sulfur are non-limiting. Most species had low phosphorus, copper and selenium, while some had magnesium and zinc levels lower than the critical limit because of low mineral content and high percolation rate of lahar deposits. Iron and molybdenum were in excess. The effect of seasonal variation was observed only in copper, sulfur and iron. Average blood mineral concentration of the animals was above critical limit, but there were no significant differences between seasons. All the animals had plasma phosphorus and magnesium above critical level; but 20 % had low copper, zinc and selenium especially in dry season possibly due to insufficient amount of these elements and excessive molybdenum and iron in most forage. Conversely, calcium in forage was high; but 40 % of the animals had low plasma calcium concentration. Although no clinical signs of mineral deficiencies were observed, supplemental feeding would be important since the condition of the pasture in lahar-laden areas is not expected to improve in the next five years. Intensified use of L. leucocephala with better mineral profile would be ideal.

• 미생물학회지
• /
• 제42권4호
• /
• pp.286-293
• /
• 2006

대전일원의 유류오염 지역의 토양으로부터 원유를 단일 탄소원으로 이용하는 총 322균주를 순수분리 하였고, 이중 생물 계면활성제(biosurfactant) 생성능이 가장 우수한 한 균주를 최종 선별하여 형태 및 생리 생화학적 특성을 조사하고 16S rRNA 염기서열을 분석을 통하여 동정한 결과 Pseudomonas sp.로 확인되어 Pseudomonas sp. G314라 명명하였다. 최종 선별된 Pseudomonas sp. G314는 암피실린, 클로람페니콜, 스펙티노마이신, 스트렙토마이신 등의 항생제와 Li, Cr, Mn 등의 중금속에 대해 강한 내성을 갖고 있었고, 최적 온도와 pH는 각각 $30^{\circ}C$와 pH 7.0으로 확인되었다. Pseudomonas sp. G314가 생성하는 생물 계면활성제의 초기 표면장력은 72 dyne/cm이었으나, 배양 7시간 후 부터는 표면장력이 최대 25 dyne/cm까지 감소되었다. Pseudomonas sp. G3l4가 생산하는 생물 계면활성제를 회수하고 농축하기 위해, 산 침전 후에 유기용매로 배양액을 추출하고 이를 감압농축하여 얻은 시료를 crude biosurfactant로 사용하여 CMC (critical micelle concentration)간을 측정한 결과 20 mg/L로 확인되었다.

• Korean Chemical Engineering Research
• /
• 제46권4호
• /
• pp.824-832
• /
• 2008

용매인 물과 마이셀을 이루지 않고 있는 계면활성제 단분자를 포함한 단분산 마이셀 용액을 통계 역학적으로 고찰하였다. 본 논문에서 논의된 모델은 물, 계면활성제 단분자와 마이셀로 이루어진 계에 대한 것이며, 계면활성제 단분자의 분배 함수와 마이셀의 분배 함수는 용매인 물과의 서로 작용을 포함하고 있다. 이 모델에서 계는 용매의 유전 상수를 갖는 이상 기체로 가정하였는데 이것은 보통 유체를 연속체로 보는 관점과 일치한다. 이 모델은 임계 마이셀 농도(CMC)가 온도에 대해 ln CMC = A+BT+C/T+DlnT와 같이 변하는 결과를 제공하여 임계 마이셀 농도의 온도 의존성을 이론적으로 해석할 수 있는 기반을 구축하였다. 이 식에서 T는 온도이고 A, V, C, D는 마이셀을 이루는 계면활성제 분자의 성질에 의존하는 상수이다.

• 대한화학회지
• /
• 제55권2호
• /
• pp.163-168
• /
• 2011

다양한 농도의 N-methyl acetamide 수용액에서 계면 활성제의 농도에 따른 계면활성제들 (sodium caprylate, sodium laurate, sodium palmitate, sodium stearate, sodium oleate, sodium dodecyl sulphate, lithium dodecyl sulphate)의 몰 전도도 변화를 $30{\pm}0.2^{\circ}C$의 일정온도에서 연구하였다. 각각의 계면활성제에 대한 임계 미셀 농도 (CMC)를 측정하였다. 수용액에 N-methyl acetamide이 공존할 때에는 여러 계면 활성제의 CMC 값이 수용액에서의 CMC 값보다 더 낮고, 미셀 형성에 대한 추진력은 소용매성과 관련되었다. N-methyl acetamide 수용액에서 양쪽성 자기-조직화를 추진하는 계면활성제-용매의 상호작용에 대해 논의하였다. 이 결과들을 설명하기 위하여 미셀 시스템에 대한 열역학적 매개변수들을 추정하였다.

• 치위생과학회지
• /
• 제19권1호
• /
• pp.31-38
• /
• 2019

Background: This study aimed to investigate the effects of critical thinking and good communication skills on the problem-solving abilities of dental hygiene students. Methods: A total of 508 dental hygiene students were convenience-sampled from 3 universities. Results: The results revealed that critical thinking had the highest intellectual fairness score of 3.60, and systematicity was the lowest at 3.19. The values for communication skills were high in reaction, social adequacy, and concentration, with an average of 3.65. Problem-solving abilities were in the following order: clarification of the problem, seeking solutions, and decision making. According to general characteristics, more extroverted personalities possessed higher levels of critical thinking, communication skills, and problem-solving abilities (p<0.01). Critical thinking scores were high (p=0.016) in students who responded that peer relationship was difficult; however, their communication skills were the lowest (p<0.001). Additionally, problem-solving abilities were highest among students who reported a difficult peer relationship (p=0.001). The higher the satisfaction with dental hygiene academics, the higher the critical thinking, communication skill, and problem-solving ability (p<0.001). Critical thinking showed a high positive correlation with variables in the following order: clarification of the problem, performing the solutions, seeking solutions, decision making, and evaluation and reflection. The communication skills were also related to these variables listed above (p<0.01). With critical thinking, confidence, watchfulness, intellectual passion/curiosity, sound skepticism, objectivity, and systematicity all influenced the problem-solving ability. Conclusion: Communication skills were influenced by noise control, putting on the other's shoe, social tensions, and efficiency, which affected the problem-solving ability. Dental clinics require dental hygienists to have critical thinking to make analytical judgments and effective communication skills to solve human relation problems with patients and care-givers. Therefore, these skills should be developed in dental hygiene students to improve their problem-solving abilities.

• 한국안전학회지
• /
• 제27권3호
• /
• pp.71-76
• /
• 2012

The coflow velocity effect on the minimum extinguishing concentration(MEC) was investigated experimentally in heptane cup-burner flames. Various inert gases($N_2$, Ar, $CO_2$, He) were added into the oxidizer to find the critical concentration and the effectiveness of the agents on flame extinction. The experimental results showed that the MECs were increased with increasing coflow velocity for most inert gases except helium, but the higher coflow velocity induced the lower burning rates of heptane. This indicated that the increase of coflow velocity resulted in the decrease of fuel velocity evaporated from fuel surface, and hence the stain rate on the reaction zone was also decreased. In the case of helium as a additive, the extinguishing concentration was independent of the coflow velocity because the heat conductivity was ten times larger than the other inert gases and flow effect by a strain rate might be compensated for heat loss to the surroundings.

• 한국안전학회지
• /
• 제24권1호
• /
• pp.21-25
• /
• 2009

Extinguishing limits of laminar ethylene/oxygen flames in both normal and inverse co-flow jet burner have been determined experimentally and computationally. An inert gas($N_2$, Ar, $CO_2$) was added into the oxidizer to find the critical concentration and the effectiveness of the agents on flame extinction. The experimental results showed that the physical aspect of inert gases was main mechanism for flame blow-out as same as cup burner test, but the flow effect should be considered to determine the extinction concentration. The numerical prediction was performed with modified WSR model and the result was in good agreement with the measurements. The experimental and numerical methods could be used for the assessment of various flame suppression agents such as minimum extinguishing concentration.

• Nuclear Engineering and Technology
• /
• 제55권7호
• /
• pp.2489-2497
• /
• 2023

Co and Eu impurities in the SSCs are nuclides that dominantly influence the neutron-induced radioactive inventory in metal and concrete radwastes (radioactive wastes) during NPP decommission. The impurity concentrations provided by NUREG/CR-3474 were used for the practical range of Co and Eu impurity concentrations to be applied to the code calculations. Metal structures near the core were evaluated to be ILW (intermediate-level waste) for the whole range of Co impurity concentration, so the boundary line between ILW and LLW (low-level waste) has no change for the whole concentration range provided by NUREG/CR-3474. Also, the boundary line between VLLW (very low-level waste) and CW (clearance waste) in the concrete shield could alter a little depending on the Eu impurity concentration within the range provided by NUREG/CR-3474. From this work, it is found that the concentration of material impurities of SSCs gives no critical impact on determining radwaste levels.