• The Korean Journal of Rheology
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• v.9 no.3
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• pp.118-123
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• 1997

검화도와 분자량이 상이한 폴리비닐 알코올을 디멜틸 설폭사이드에 녹여 폴리비닐 알코올/디멜틸 설폭사이드 용액을 준비하고 동적 유변학적 특성에 대한 시간과 온도 의존성 을 고찰하였다. 고농도 폴리비닐 알코올 용액의 유변학적 특성은 시간 의존성을 보여주었다. 복합점도와 저장탄성률은 시간에 따라 증가하였다. 또한 저장 탄성률과 손실탄성률의 그래 프에서 저장탄성률은 신간에 따라 증가하였으나 기울기는 시간에 따라 증가하였다. 또한 저 장탄성률과 손실탄성률의 그래프에서 저장탄성률은 시간에따라 증가하였으나 기울기는 시간 에 따라 감소하였다. 유변학적 특성의 시간 의존성은 분자량이 높을수록, 측정온도가 높을수 록 더 두드러지게 나타났다.

• The tire
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• s.61
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• pp.16-19
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• 1975

무우니이점도 30에서 70까지의 천연고무(이하 NR이라고 약)와 합성 시스-1,4-포리이소프렌(이하 IR이라고 약)의 완화탄성률에 대해서 검토했다. 완화탄성률은 -50℃로부터 90℃이며 시간 3초로부터 3,000초에 긍해서 측정했다. 동일한 무우니이점도로서 어느 온도에 있어서도 IR의 완화탄성률은 NR에 비하면 작으며 따라서 IR은 부드럽게 촉감된다고 생각된다. NR과 IR의 각종온도에서의 완화탄성률과 시간의 관계는 같은 환산계수를 사용해서 중합이 가능했었다. 얻어진 합성곡선에 대해서 특히 종단역에 있어서 NR의 완화탄성률이 IR에 비해서 크다. 이것은 같은 무우니이점도로서 NR쪽이 IR에 비하여 높은 평균분자량과 넓은 분자량분포를 가지기 때문이라고 생각된다.

• Polymer(Korea)
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• v.24 no.6
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• pp.810-819
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• 2000

Poly(p-hydroxybenzoate) (PHB)/poly(ethylene terephthalate) (PET) 8/2 thermotropic liquid crystalline copolyester, poly(ethylene 2,6-naphthalate) (PEN), and PET ternary blend was spun to fiber by melt spinninB process, and tensile properties of the fibers were measured. The matrix of the fibers, PET and PEN, were dissolved in ο-chlorophenol at 55$^{\circ}C$ for 2 hours, and the liquid crystalline polymer fibrils were observed using a scanning electron microscope. Halpin-Tsai equation for modulus calculation of short fiber reinforced composite and the rule of mixture for continuous reinforcement composite were modified, and the tensile modulus were calculated and compared with experimental modulus. To minimize difference between the theoretical and the experimental moduli, dimensionless viscosity constant (K) was given and used to modify two equations. The theoretical tensile modulus using the newly modified equations presentel a similar to the experimental tensile modulus of composite, and the modified equations presented a unique way to determine the tensile modulus of the liquid crystalline polymer reinforced thermoplastic composites.

• Proceedings of the Korea Information Processing Society Conference
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• 2021.11a
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• pp.731-732
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• 2021

인쇄 적성 증진제는 식품용 3D 프린팅에서 겔화 소재의 인쇄 적성을 향상시키는 요소 중 하나이다. 이 때, 인쇄 적성 증진제의 평가는 전단응력을 받을 때 일어나는 변형의 정도를 나타내는 전단탄성률 기반으로 한다. 그러나, 전단 탄성률 측정은 식품 원재료의 다양함으로 인해 소재별로 측정하는데 많은 시간과 비용이 소요되는 단점이 있다. 이에 본 연구에서는 FCN과 RNN을 사용하여 전단탄성률을 예측하는 신경망 설계를 제안함으로써 인쇄 적성 증진제의 전단탄성률을 측정하는 시간과 비용을 절감하고자 한다.

• The Korean Journal of Nuclear Medicine
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• v.37 no.6
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• pp.355-363
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• 2003

Purpose: Regional contractility can be calculated using the regional volume change of left ventricle measured by gated myocardial SPECT image and curve of central artery pressure obtained from radial artery pressure data. In this study, a program to obtain the regional contractility was developed, and reproducibility of regional contractility measurement was assessed. Materials and Methods: Seven patients(male:female=5:2, $58{\pm}11.9$ years) with coronary artery diseases underwent gated Tc-99m MIBI myocardial SPECT twice without delay between two scans. Regional volume change of left ventricle was estimated using CSA (Cardiac SPECT Analyzer) software developed in this study. Regional contractility was iteratively estimated from the time-elastance curve obtained using the time-pressure curve and regional time-volume curve. Reproducibility of regional contractility measurement assessed by comparing the contractility values measured twice from the same SPECT data and by comparing those measured from the pair of SPECT data obtained from a same patient. Results: Measured regional contractility was $3.36{\pm}3.38{mm}Hg/mL$ using 15-segment model, $3.16{\pm}2.25{mm}Hg/mL$ using 7-segment model, and $3.11{\pm}2.57{mm}Hg/mL$ using 5-segment model. The harmonic average of regional contractility value was almost identical to the global contractility. Correlation coefficient of regional contractility values measured twice from the same data was greater than 0.97 for all models, and two standard deviations of contractility difference on Bland Altman plot were 1.5%, 1.0%, and 0.9% for 15-, 7-, and 5-segment models, respectively. Correlation coefficient of regional contractility values measured from the pair of SPECT data obtained from a same patient was greater than 0.95 for all models, and two standard deviations on Bland Altman plot were 2.2%, 1.0%, and 1.2%. Conclusion: Regional contractility of left ventricle measured using developed software in this study was reproducible. Regional contractility of left ventricle will be a new useful index for myocardial function after analysis of the clinical data.

• Journal of the Mineralogical Society of Korea
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• v.13 no.3
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• pp.138-146
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• 2000

Using the ultrasonic interferometry on the single crystal MgO-periclase, adiabatic bulk moduli were determined to be 163.2 GPa and 162.6 GPa from (100) and (110) lattice plane measurements, respectively. Density was measured on polycrystalline MgO by the X-ray diffraction technique. Results from this study were compared with the previously reported values. Further, the present results were converted to the isothermal bulk moduli and, then compared with the published data available including the energy dispersive X-ray diffraction result which was performed on the same single crystal MgO. The principle and techniques ultrasonic interferometry were introduced too.

• The Korean Journal of Nuclear Medicine
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• v.35 no.3
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• pp.152-160
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• 2001

Purpose: We tried to establish the reproducibility of the measurement of maximal elastance (Emax) and to compare the degree of the reproducibility of two estimation methods: single pressure-volume loop method and parameter optimization method. Materials and methods: In 47 patients (42 males and 5 females, $53{\pm}10$ years old) with suspected coronary artery disease (election fraction; 22-68%), gated Tc-99m MIBI myocardial SPECT and arterial tonometry were acquired. In 11 patients among these 47 patients, gated SPECT and tonometry were performed twice consecutively with patients in situ. Emax and void volume (Vo) were estimated using single pressure-volume loop method of Lee and parameter optimization method based on linear approximation of Yoshizawa. Correlation between the consecutive measurements by each method and correlation between the two estimation methods were compared. Results: Reproducibility of Emax (r=0.96) and Vo (r=0.99) by single pressure-volume method was better than the reproducibility of Emax (r=0.89) and Vo (r=0.64) by parameter optimization method. Correlations of Emax and Vo were fair between the two methods. The correlation of Emax (r=0.77) was better than that of Vo (r=0.55). Conclusion: Reproducibility of Emax measurement by single pressure-volume loop method using gated myocardial SPECT and arterial tonometry was excellent. Reproducibility by parameter optimization method was also fair but was less than that achieved by single pressure-volume method.

• Journal of the Korean Vacuum Society
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• v.10 no.4
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• pp.387-395
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• 2001

The elastic modulus and the structural evolution were examined with the film thickness in polymeric, hard, graphitic diamond-like carbon (DLC) films. The DLC films used in the present study were prepared by radio frequency plasma assisted chemical vapor deposition (r.f.-PACVD) from $C_6H_6\;and\;CH_4$ gas. Elastic modulus of very thin DLC film was measured by free overhang method. This method has an advantage over the other methods. Because the substrate was removed by etching technique, the measured value is not affected by the mechanical property of the substrate. The structural evolution was investigated by the G-peak position of the Raman spectrum. The polymeric and graphitic films exhibited the decreased elastic modulus with decreasing film thickness. In polymeric films, the reason was that more polymeric film had been deposited in the initial stage of the film growth and in graphitic film more graphic films which had been deposited in the initial stage decreased the elastic modulus. The G-peak position of the Raman spectrum confirmed this result. On the other hand, the hard film showed the constant elastic modulus regardless to the film thickness. The structural change was not observed in this range of the film thickness.

• Journal of agriculture & life science
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• v.46 no.6
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• pp.75-86
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• 2012

In this study, eco-friendly hybrid composite boards were manufactured from green tea, 3 kinds of charcoals and wood fiber for developing interior materials to reinforce the strength performances and the functionalities in addition to performances of the hybrid composite boards composed of green tea and wood fiber. The effects for the kind and the component ratio of raw materials on dynamic MOE (modulus of elasticity) were investigated, and static bending strength performances were nondestructively estimated. Dynamic MOEs were highest in the hybrid composite boards composed of green tea, fine charcoal and wood fiber on the whole. However, the difference caused by the kind of charcoals was small. These values decreased with increasing component ratios of green tea and charcoals. The hybrid composite boards using $E_1$ grade urea resin had the higher values than those using $E_0$ grade urea resin, however the difference between them markedly decreased than that of hybrid composite board composed of green tea and wood fiber, and it was found that these values were markedly improved than those of the hybrid composite boards composed of green tea and wood fiber. There were mostly high correlations with significance at 1% level between dynamic MOEs and static bending strength performances, and this means that the static bending strength performances can be estimated from dynamic MOE.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.2
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• pp.407-412
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• 1990

Elastic modulus of unidirectional short fiber composite has theoretically derived with the consideration of Poisson's ratios of matrix and fiber. Unidirectional short fiber composite is modeled as an aggregate of grains developed by Kerner. Under the assumption of extra strain at fiber ends, the strain distribution along the fiber's length is determined, and the elastic modulus is derived from this distribution. For the consideration of effects of Poisson's ratio, Kerner's results for particulate composites are adapted as boundary conditions. The effect of differences in Poisson's ratio of fiber and matrix on elastic modulus is studied. Proposed equation shows a good agreement with experimental data of Halpin and Tock, et al.