• 한국의상디자인학회지
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• 제7권3호
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• pp.75-81
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• 2005

The experiment aimed at knowing the effect of physiology and psychology according to season on color preference. Two tests, one of the spring and the other of the autumn was conducted. Seventy subjects with normal color vision served as subjects. The subjects entered a bioclimatic chamber controlled at a temperature of $25\pm1^{\circ}C$, a relative humidity of $50\pm5\%$ and a light of 1000 1x. The subjects wearing white shirts and trousers sat quietly on a sofa for one our. Sensation from warm to cool colors might be possibly different individually Therefore, a subject asked to array 41 randomly placed cloth colors from very warm to very cool colors during rest quietly for one our. All subjects arrayed these cloth colors in the order from red through yellow and green to blue, which had the reproducibility. After rest, they were instructed to choose a single one out of 41 cloth colors, preferred by themselves, every 10min during one our 0-ring test were measured to red, yellow, white, blue, black, favorite color, and dislike color. Most subjects preferred warmer color in April than in December. Tympanic temperature was significantly lower in December than in April. Finger presser was significantly higher in like color than in dislike color but it was no significant differences between spring and autumn. The preferring the warm color in April toward summer when basal metabolic rate is decreased than in December toward winter when it is increased can explain that physiology reaction by load error between actual core temperature and set-point induces psychological reaction to pursue visual alliesthesia. Our present experiment revealed that the preferred color could be determined by the relationship between the internal temperature and its set point according to season. It should be emphasized that the alliesthesia was observed also in the realm of visual system.

• 한국소음진동공학회논문집
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• 제17권1호
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• pp.72-79
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• 2007

정밀 장비 운전시 지반진동 절연을 목적으로 널리 사용되는 공압제진대는 정밀 장비에서 요구하는 지반진동 규제의 강화에 따라 보다 개선된 절연성능을 요구받는다. 수동형 공압제진대의 경우, 제진대의 설계 변수들을 이용하여 그 성능을 개선하고 있으나, 제진대의 고유진동수 및 그 부근에서의 절연 성능 향상에는 한계가 있다. 이 연구에서는 진폭 의존성 등의 비선형성을 가지는 공압제진대에 대하여 비선형 강인성 능동제어이론인 시간지연 제어 기법을 적용하여 고유진동수 및 그 부근에서의 절연성능을 향상시키고자 한다. 공압제진대에 시간지연 제어기법을 적용하는 과정 및 능동제어 이론 적용에 따른 절연 성능 향상에 대한 모사실험 결과를 기술하고자 하며, 실험을 통하여 그 유효성 보이고자 한다.

• Journal of Biosystems Engineering
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• 제8권1호
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• pp.38-46
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• 1983

This study was carried out to investigate the possibility of improving the performance of a kerosene engine with water addition. The engine used in this study was a single-cylinder, four-cycle kerosene engine with the compression ratio of 4.5. Water could be successfully added into the inlet manifold by an extra carburetor for the volumetric ratios of 5, 10, 20, and 30 percents. Variable speed tests at wide-open throttle were performed for five speed levels in the range of 1,000 to 2,200rpm for each fuel type. Volumetric efficiency and brake specific fuel consumption were determined, and brake thermal efficiency based on the lower heats of combustion of kerosene was calculated. To examine variation in fuel consumption, CO concentration, and cooling water temperature, part load tests were also performed. The results obtained are summarized as follow. (1) Brake torque increased almost in proportion to volumetric efficiency. But the ratio of increase in torque was greater than that of volumetric efficiency. Mean torque over the speed range of 1,000 to 2,200rpm increased 1, 3, 7, and 2 percents for 5, 10, 20, and 30 percents water addition, respectively. The increase in brake torque with water addition was greater at lower speeds. (2) Mean brake specific fuel consumption over the speed range of 1,000 to 2,200rpm decreased 1, 2, 3, and 3 percents for 5, 10, 20, and 30 percents water addition, respectively. (3) Mean temperature of cooling water over the speed range of 1,000 to 2,200rpm decreased 2, 4, 8, and 12 percents for 5, 10, 20, and 30 percents water addition, respectively. (4) The effects of decreasing CO concentration in the exhaust emissions with water addition were significant. At the speed range of 1,000 to 2,200rpm, CO concentration in the exhaust emissions decreased 2, 10, 23, percents for 5, 10, and 20 percents water addition, respectively. (5) Deposits were not discovered in the combustion chamber during the experiment. However, a little rust was formed in the water-supply carburetor.

• Restorative Dentistry and Endodontics
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• 제22권1호
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• pp.413-427
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• 1997

Porphyromonas endodontalis and Prevotella intermedia are black-pigmented anaerobic gram negative rods which have been isolated from infected root canals and submucous abscesses of endodontic origin. And they are associated with clinical symptoms such as pain, percussion, and foul odor. It has been reported that there are 3 serotypes according to capsule membrane in P. endodontalis and 2 DNA homology groups and 3 serotypes in P. intermedia, but there is no data available regarding genetic diversity for the species P. endodontalis and P. intermedia. The purpose of this study is to investigate genetic diversities between individual strains of P. endodontalis and P. intermedia which are indistinguishable by serotyping and biotyping using bacterial DNA restriction endonuclease analysis. 45 teeth with at least one clinical symptoms, with single canal, and with pulp necrosis were sampled. For sampling bacteria, access cavity was prepared after disinfecting tooth and its surroundings. Then the paper point was inserted to the apex of the canal, leave there for 15 seconds, and finally it was placed into PRAS Ringer's solution and PBS solution. P. endodontalis and P. intermedia were identified by biochemical test and IIF after subculturing black and brown colonies which were produced after 7 days of incubation on BAP in anaerobic chamber. P. endodontalis and P. intermedia strains were grown in BHI broth and whole genomic DNA was extracted by phenol-chloroform extraction technique and digested by restriction endonuclease, Eco RI and Pst I. The resulting DNA fragments were separated by agarose gel electrophoresis, stained with EtBr and photographed under UV light. The results were as follows : 1. In both P. endodontalis and P. intermedia, different serotypes could be found within a root canal of same patient. 2. There were obvious genetic heterogeneity within a patient and within a serotype in both P. endodontalis and P. intermedia. 3. P. endodontalis serotype c, isolated from different patients, exhibited limited genotypic diversity.

• 한국자동차공학회논문집
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• 제17권1호
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• pp.105-113
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• 2009

The performance of a direct-injection type diesel engine often depends on the strength of swirl or squish, shape of combustion chamber, the number of nozzle holes, etc. This is of course because the combustion in the cylinder was affected by the mixture formation process. In this paper, combustion process of biodiesel fuel was studied by employing the piston which has several grooves with inclined plane on the piston crown to generate swirl during the compression stroke in the cylinder in order to improve the atomization of high viscosity fuel such as biodiesel fuel and toroidal type piston generally used in high speed diesel engine. To take a photograph of flame, single cylinder, four stroke diesel engine was remodeled into two stroke visible engine and high speed video camera was used. The results obtained are summarized as follows; (1) In the case of toroidal piston, when biodiesel fuel was supplied to plunger type injection system which has very low injection pressure as compared with common-rail injection system, the flame propagation speed was slowed and the maximum combustion pressure became lower. These phenomena became further aggravated as the fuel viscosity gets higher. (2) In the case of swirl groove piston, early stage of combustion such as rapid ignition timing and flame propagation was activated by intensifying the air flow in the cylinder. (3) Combustion process of biodiesel fuel was improved by the reason mentioned in paragraph (2) above. Consequently, the swirl grooves would also function to improve the combustion of high viscosity fuel.

• 한국분무공학회지
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• 제25권1호
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• pp.8-14
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• 2020

Recently, 1-D model-based engine development using virtual engine system is getting more attention than experimental-based engine development due to the advantages in time and cost. Injection rate profile is the one of the main parameters that determine the start and end of combustion. Therefore, it is essential to set up a sophisticated model to accurately predict the injection rate as starting point of virtual engine system. In this research, procedure of 1-D model setup based on AMESim is introduced to predict the dynamic behavior and injection rate of diesel injector. As a first step, detailed 3D cross-sectional drawing of the injector was achieved, which can be done with help of precision measurement system. Then an approximate AMESim model was provided based on the 3D drawing, which is composed of three part such as solenoid part, control chamber part and needle and nozzle orifice part. However, validation results in terms of total injection quantity showed some errors over the acceptable level. Therefore, experimental work including needle movement visualization, solenoid part analysis and flow characteristics of injector part was performed together to provide more accuracy of 1-D model. Finally, 1-D model with the accuracy of less than 10% of error compared with experimental result in terms of injection quantity and injection rate shape under normal temperature and single injection condition was established. Further work considering fuel temperature and multiple injection will be performed.

• Restorative Dentistry and Endodontics
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• 제26권5호
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• pp.379-386
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• 2001

This study was performed to evaluate the sealing ability of various retrograde filling materials by using bacterial penetration and dye penetration test. One hundred and forty extracted human teeth with single, straight canals and mature apiece were collected and used for this study. All canals were instrumented using an engine driven Ni-Ti file (ProFile). After removing 3mm from the apex of tooth, a standardized 3mm root end cavity was prepared using an ultrasonic instrument. The 70 teeth were randomly divided into 7 groups : 6 groups for retrograde filling using Super-EBA, ZOE, Chelon-Silver, IRM, ZPC and amalgam. The 7th group was used as a negative control. Nail varnish was applied to all external root surfaces to the level of the reseated root ends to prevent lateral microleakages. The specimens were then sterilized in an ethylene oxide sterilizer for 24 hours. 2 mm of the reseated root was immersed in a culture chamber containing a Tripticase Soy Broth with a phenol red indicator. The coronal access of each specimen was inoculated every 72 hours with suspension of Proteus vulgaris. The culture media were observed every 24hours for color change indicating bacterial contamination. The specimens were observed for 4weeks. The remaining 70 teeth were submitted to a dye penetration test. The canals of all teeth were first sealed with AH26 and obturated using an Obtura II system. Root resection, root end preparation and retrograde filling was performed as above. All specimens were suspended in 2% methylene blue dye for 72 hours before being ion gitudinally split. The degree of dye penetration was then measured using a stereomicroscope at 10 magnification and evaluated. The results were as floows : 1. In the bacterial penetration, the degree of leakage was the lowest in the Super-EBA, followed by, in ascending order, ZOE, Chelon-Silver IRM and ZPC. The amalgam showed highest bacterial leakage of all(p<0.01). 2. In the dye penetration, the degree of microleakage was the lowest in the Chelon-Silver and Super-EBA, followed by, in ascending order, IRM, ZPC. The ZOE and amalgam showed the highest microleakage of all (p<0.05). These results suggested that the eugenol based cement, Super-EBA, have excellent sealing ability as a retrograde filling material.

• 대한기계학회논문집B
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• 제35권10호
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• pp.1083-1088
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• 2011

임펠러 및 플로팅 링 실의 형상이 원심 펌프의 성능에 미치는 영향을 수류 시험 결과를 토대로 연구하였다. 연구 대상이 된 펌프는 30 톤급 및 75 톤급 액체로켓엔진용으로 개발된 단단 원심형 펌프로 연소실에 추진제(액체산소, 케로신)를 공급하는 터보펌프의 일부이다. 펌프의 양정은 임펠러 출구 폭 및 날개 개수, 날개의 출구 각도의 영향을 받는 것으로 나타났다. 또한 개발된 펌프는 플로팅 링 실의 간극에 따라 그 효율에 차이가 있었으며, 크기 증가에 따른 효율 증가 효과는 크게 나타나지 않았다.

• Elastomers and Composites
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• 제55권1호
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• pp.51-58
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• 2020

In this study, the thermal oxidation of raw natural rubber (NR) was investigated under controlled conditions by optical image and fourier transform infrared (FT-IR) analysis. The thermal oxidation was performed on a transparent thin film of raw NR coated on a KBr window in a dark chamber at 80℃ under low humidity conditions to completely exclude moisture and restrict light oxidation. Images of the thin film of raw NR were obtained before and after thermal oxidation. FT-IR absorption spectra were measured in the transmission mode at different thermal exposure times. The thermal oxidation of NR was examined by the changes in the absorption peaks at 3449, 1736, 1447, 1377, 1242, 1072, and 833 cm^-1, which corresponded to a hydroxyl group (-OH), a carbonyl group (-C=O) from an aldehyde and a ketone, a methylene group (-CH₂-), a methyl group (-CH₃), a carbon-oxygen single bond (-C-O) from an epoxide, a carbon-oxygen bond (-C-O) from an ether, an alcohol, a peroxide, or a cyclic peroxide, and a cis-methine group (cis-CCH₃=CH-), respectively. In the initial stage of thermal oxidation, two different types of free radicals were produced quickly and randomly by the homolytic cleavage of a double bond and allylic hydrogen abstraction. Aldehydes and ketones were formed from chain scissions of the double bonds and alcohols were produced from allylic hydrogen abstraction at the methylene or methyl groups. Two reactions seemed to proceed competitively with each other. At a later stage, oxidative crosslinks seemed to dominate through the combination of free radicals such as an allyl radical (CH=CHCH₂·), alkoxy radical (RO·), and peroxy radical (ROO·) and the reaction of a hydroperoxide (-ROOH) with a double bond. The image obtained after thermal oxidation showed hardening without cracks. Based on these observations, a plausible two-step mechanism was suggested for chain hardening caused by the thermal oxidation.

• 한국분무공학회지
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• 제16권3호
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• pp.119-125
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• 2011

Due to the oxygen contents in biodiesel, application of the fuel to compression ignition engines has significant advantages in terms of lowering PM formation in the combustion chamber. In recent days, considerable studies have been performed to extend the low temperature combustion regime in diesel engines by applying biodiesel fuel. In this work, low temperature combustion characteristics of biodiesel blends in dilution controlled regime were investigated at a fixed engine operating condition in a single cylinder diesel engine, and the comparisons of engine performances and emission characteristics between biodiesel and conventional diesel fuel were carried out. Results show that low temperature combustion can be achieved at $O_2$ concentration of around 7~8% for both biodiesel and diesel fuels. Especially, by use of biodiesel, noticeable reduction (maximum 50% of smoke was observed at low and middle loads compared to conventional diesel fuel. In addition, THC(total hydrocarbon) and CO(Carbon monoxide) emissions decreased by substantial amounts for biodiesel fuel. Results also indicate that even though about 10% loss of engine power as well as 14% increase of fuel consumption rate was observed due to lower LHV(lower heating value) of biodiesel, thermal efficiencies for biodiesel fuel were slightly elevated because of power recovery phenomenon.