• 한국자동차공학회논문집
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• 제22권6호
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• pp.104-112
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• 2014

Generally, numerical approaches of evaluation for vehicle seat comfort have been studied without considering time-dependent characteristics and the only seating moment have been considered in seat design. However, the comfort not only at the seating moment but also in the long-term should be evaluated because the passengers are sitting repeatedly on the seat to drive the vehicle for hours. So, the aim of this paper is to carry out a quantitative evaluation of the time-dependent mechanical characteristics of seat foams and to suggest a process for predicting the viscoelastic deformation of seat foam in response to long-term driving. To characterize the seat materials, uniaxial compression and tension tests were carried out for the seat foam and stress relaxation tests were performed for evaluating the viscoelastic behavior of the seat foam. A unit solid element model was used to verify the reliability of the material model with respect to the compression behavior of the seat foam. It is not straightforward to evaluate the time-dependent compression of foams using the explicit solver because the viscoelastic material model is limited. To use the explicit solver, the material model must be modified using stress-degradation data. Normalized stress relaxation moduli were added to the stress-strain curves obtained under static conditions to achieve a time-dependent set of stress-strain relations that were compatible with the implicit solver. There was good agreement between the analysis results and experimental data.

• 한국방재학회 논문집
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• 제10권2호
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• pp.39-46
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• 2010

본 연구에서는 조골재, 세골재 및 시멘트량을 달리한 포장용 콘크리트 시편에 대한 강도시험을 통해 물성 정량화 모델식을 제시하였다. 관계식으로는 압축강도와 휨강도, 압축강도와 쪼갬인장강도, 압축강도와 탄성계수 그리고 휨강도와 쪼갬인장강도의 상관관계식을 제시하였다. 모델식에 사용된 데이터는 총 61~81개 조합으로서, 1개 조합에 사용된 시편은 3-4개이었다. 아울러 제시된 상관관계 모델식을 사용하여 고속도로 10개 현장과 국도 4개 현장의 LTPP 구간에서 얻은 코어시편의 탄성계수를 추정하는 절차를 제시하였다. 변동성을 감안하여 본 연구에서는 각 LTPP 구간을 대표하는 탄성계수로서 압축강도에서 탄성계수로 환산한 값과 코어 시편을 사용하여 스트레인게이지에 의해 측정된 탄성계수의 평균값을 사용함으로 인해 코어시편으로부터 발생될 수 있는 측정오차를 줄일 수 있는 방안을 제시하였다.

• Journal of Pharmaceutical Investigation
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• 제41권2호
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• pp.83-90
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• 2011

Main objectives of this study were to investigate the effects of a lubricant, magnesium stearate, as blended in a hydrophilic matrix tablet and to identify significant factors using a tablet ejection force and a swelling property. The characteristics of tablet ejection were evaluated with three different compression forces (30, 40, and 60 MPa) and two controlled factors, amount of magnesium stearate and its mixing time. A hydrophilic model drug (terazosin HCl dihydrate) was regarded as a default factor. Tablet swelling was also evaluated. The optimal amount of PEG compared to PEO was set to be 88.50% w/w. As the amount of magnesium stearate was varied from 0.79% to 2.20% w/w, the amount of PEO and PEG was adjusted to meet the tablet's total weight while maintaining the ratio between the two excipients constant. As the mixing time of magnesium stearate was increased, the tablet ejection force and the swelling property were decreased. As the amount of magnesium stearate was increased, the tablet ejection force and the swelling property were decreased since the increased mixing time and the amount of magnesium stearate induced hydrophobic properties of the matrix tablet more effectively. The ejection force of the tablet increased as a result of increase in the compression force, which means that the breaking of tablet/die-wall adhesion energy was also increased when the compression energy was increased. The results gavea valuable guide how to choose suitable amount of the lubricant with processing conditions for the development of hydrophilic matrix formulations.

• 한국정보처리학회논문지
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• 제2권5호
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• pp.677-690
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• 1995

본 논문에서는 블럭정렬과 선두 이동법에 의해 처리된 계열을 VF(Variable to Fixed)형 산술부호로 압축하는 방법을 제시한다. 길이 N으로 분해된 부분열을 1기호씩 순회시킨 후 사전식 순서로 정렬한다. 순회정렬된 부분열은 국소적으로 유사기호가 밀 집되기 때문에 이 성질을 활용하기 위하여 선두 이동법을 적용한다. 이와 같이 전처리 된 계열에 대해 오류전파를 1 부호어 이내로 제한할 수 있는 VF형 산술부호 로 엔트 로피 부호화한다. VF형 산술부호의 효율은 고정 크기의 부호어 집합을 어떻게 분할하 는가가 관건이다. 제안하는 VFAC(VF Arithmetic Code)는 새로 설정되는 정보원 기호에 대하여 완전분할을 이루게 하고, 반복적인 그레이 변환을 이용하여 발생기호의 확률을 효과적으로 나타낸다. 제안 방식의 성능을 컴퓨터 시뮬레이션을 통하여 엔트로피, 압 축율 및 처리속도의 측면에서 기존의 방식과 비교 분석한다.

• 전기전자학회논문지
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• 제21권1호
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• pp.39-45
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• 2017

영상 압축은 데이터베이스에서 전송과 저장의 응용에 매우 중요한 분야이다. 비디오나 디지털 영상 응용에서 긴 탭의 필터를 사용하면 의미 있는 정도의 코딩이득은 얻지만 하드웨어의 복잡도를 증가시킨다. 우리는 한 쌍의 쌍직교 성질의 부 분할의 영상을 얻기 위하여 웨이브렛 변환을 사용한다. 첫째, 짧고 주요한 대칭 분석의 구현을 1차원 경우에 제시하였다. 둘째, 원래의 영상이 부대역 필터뱅크를 사용하여 다른 스케일로 분해되었다. 셋째, 본 논문에서 McClellan 변환을 사용하여 2차원의 쌍직교 필터를 얻는 기법을 제시하였다. 제시하는 웨이브렛 기저들이 영상압축에 사용되는 웨이브렛 변환에 효과적으로 사용될 수 있음을 보였다. 쌍직교 필터들의 성능 비교표로부터 웨이브렛 기저의 영상에 대한 응용에서는 우리는 실제적으로 ortho-normal 필터에 근사한 필터를 사용한다.

• Steel and Composite Structures
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• 제32권3호
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• pp.361-372
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• 2019

Tubular joints are used in the construction of offshore structures and other land-based structures because of its ease of fabrication. These joints are subjected to different environmental loadings in their lifetime. At the time of fabrication or modification of an existing offshore platform, tubular joints are usually strengthened to withstand the environmental loads. Currently, various strengthening techniques such as ring stiffeners, gusset plates are employed to strengthen new and existing tubular joints. Due to some limitations with the present practices, some new techniques need to be addressed. Many researchers used Fibre Reinforced Polymer (FRP) to strengthen tubular joints. Some of the studies were focused on axial compression of Glass Fibre Reinforced Polymer (GFRP) strengthened tubular joints and found that it was an efficient technique. Earlier, the authors had performed studies on Carbon Fibre Reinforced Polymer (CFRP) strengthened tubular joint subjected to axial compression. The study steered to the conclusion that FRP composites is an alternative strengthening technique for tubular joints. In this work, the study was focused on axial compression of Y-joint and in plane and out of plane bending of T-joints. Experimental investigations were performed on these joints, fabricated from ASTM A106 Gr. B steel. Two sets of joints were fabricated for testing, one is a reference joint and the other is a joint strengthened with CFRP. After performing the set of experiments, test results were then compared with the numerical solution in ANSYS Parametric Design Language (APDL). It was observed that the joints strengthened with CFRP were having improved strength, lesser surface displacement and ovalization when compared to the reference joint.

• 한국수소및신에너지학회논문집
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• 제34권2호
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• pp.226-233
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• 2023

In this study, we compared the performance of several refrigeration cycles using different refrigerants and utilizing the cold heat of liquefied natural gas (LNG) for the liquefaction of carbon dioxide. The final conditions for the liquefied CO₂ were set to -20℃ and 20 bar. The refrigerants used included R404a, ammonia, propane, and propylene using a vapor recompression refrigeration cycle. For the refrigeration cycle, the CO₂ at room temperature and pressure was compressed in a two-stage compression process with an intermediate cooling stage using a refrigeration unit. To compare with the liquefaction process using refrigeration, we compressed the CO₂ to 8 bar in a single compression stage and cooled it to around -50℃ using the cold heat of the LNG before liquefying it. Results showed that using ammonia as the refrigerant required the least amount of compressor power for the liquefaction process, and the heat transfer area of the evaporator was the smallest when using propylene as the refrigerant. Using the cold heat of LNG instead of refrigeration using R404a resulted in approximately 69% less energy consumption.

• Geomechanics and Engineering
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• 제28권2호
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• pp.117-133
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• 2022

Determination of the mechanical behaviour of jointed rock masses has been a challenge for rock engineers for decades. This problem is more pronounced for non-persistent jointed rock masses due to complicated interaction of rock bridges on the overall behaviour. This paper aims to study the effect of a non-persistent joint set configuration on the mechanical behaviour of rock materials under both uniaxial and biaxial compression tests using a discrete element code. The numerical simulation of biaxial compressive strength of rock masses has been challenging in the past due to shortcomings of bonded particle models in reproducing the failure envelope of rock materials. This problem was resolved in this study by employing the flat-joint contact model. The validity of the numerical model was investigated through a comprehensive comparative study against physical uniaxial and biaxial compression experiments. Good agreement was found between numerical and experimental tests in terms of the recorded peak strength and the failure mode in both loading conditions. Studies on the effect of joint orientation on the failure mode showed that four zones of intact, transition to block rotation, block rotation and transition to intact failure occurs when the joint dip angle varies from 0° to 90°. It was found that the applied confining stress can significantly alter the range of these zones. It was observed that the minimum strength occurs at the joint dip angle of around 45 degrees under different confining stresses. It was also found that the joint orientation can alter the post peak behaviour and the lowest brittleness was observed at the block rotation zone.

• Restorative Dentistry and Endodontics
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• 제46권4호
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• pp.59.1-59.14
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• 2021

Objectives: This study compared the Biodentine, MTA Repair HP, and Bio-C Repair bioceramics in terms of bond strength to dentin, failure mode, and compression. Materials and Methods: Fifty-four slices obtained from the cervical third of 18 single-rooted human mandibular premolars were randomly distributed (n = 18). After insertion of the bioceramic materials, the push-out test was performed. The failure mode was analyzed using stereomicroscopy. Another set of cylindrically-shaped bioceramic samples (n = 10) was prepared for compressive strength testing. The normality of data distribution was analyzed using the Shapiro-Wilk test. The Kruskal-Wallis and Friedman tests were used for the push-out test data, while compressive strength was analyzed with analysis of variance and the Tukey test, considering a significance level of 0.05. Results: Biodentine presented a higher median bond strength value (14.79 MPa) than MTA Repair HP (8.84 MPa) and Bio-C Repair (3.48 MPa), with a significant difference only between Biodentine and Bio-C Repair. In the Biodentine group, the most frequent failure mode was mixed (61%), while in the MTA Repair HP and Bio-C Repair groups, it was adhesive (94% and 72%, respectively). Biodentine showed greater resistance to compression (29.59 ± 8.47 MPa) than MTA Repair HP (18.68 ± 7.40 MPa) and Bio-C Repair (19.96 ± 3.96 MPa) (p < 0.05). Conclusions: Biodentine showed greater compressive strength than MTA Repair HP and Bio-C Repair, and greater bond strength than Bio-C Repair. The most frequent failure mode of Biodentine was mixed, while that of MTA Repair HP and Bio-C Repair was adhesive.

• 대한전자공학회논문지SP
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• 제39권5호
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• pp.486-493
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• 2002

본 논문에서는 웨이블릿 영역에서 각 부밴드에 대한 영역별 대역간 양방향 예측과 확장된 SPIHT (set partition in hierarchical trees)를 이용한 효율적인 인공위성 다분광 화상데이터의 압축 방법을 제안하였다. 이 방법에서는 가시광선 영역과 적외선 영역에서 다른 대역과 분광적 상관성이 큰 대역을 기준대역 (feature band)으로 각각 결정하고, 이 대역들에 대해 웨이블릿 변환 (wavelet transform, WT)을 행한 후 SPIHT를 행하여 부호화함으로써 대역내 (intraband) 중복성을 제거한다. 기준대역과 대역간 상관성이 큰 예측대역 (prediction band)들에 대해서는 웨이블릿 변환을 행한 후, 각 대역의 기저밴드의 대역별 특성을 이용하여 영역분류를 하고, 각 부밴드에 대한 영역별 대역간 양방향 예측 (classified interband bidirec- tional prediction)을 행함으로써 대역간 (interband) 중복성을 제거하여 압축 효율을 향상시킨다. 또한 확장된 SPIHT의 부호화 효율을 높이기 위해 예측오차의 최대값에 따라 재배열된 대역들에 대해 확장된 SPIHT를 행하여 예측오차를 부호화함으로써, 예측에 따른 오차를 보상하여 화질을 향상시킨다. 실제 다분광 화상데이터에 대한 모의 실험을 통하여 제안한 방법의 부호화 효율이 기존의 방법에 비하여 우수함을 확인하였다.