• 대한치과기공학회지
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• 제21권1호
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• pp.5-14
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• 1999

Glass ceramics for dental crown prosthesis were prepared by crystallization of CaO-MgO-SiO2-$P_2O_5-TiO_2$ glasses. Their crystallization behaviors have been investigated as a function of heattreatment temperature, holding time and chemical composition in relation to mechinical properties. Crystallization peak temperatures were determined by differential thermal analysis(DTA). Crystalline phases and mircostructures of heat-treated sample were determined by the means of powder X-ray diffraction(XRD) and scanning electron microscopy(SEM). The final crystalline phase assemblages and the microstructures of the samples were found to be dependent on glass compositions, heattreatment temperature, and holding time. 1st crystallization peak temperature(TP), affected strongly by apatite, was found to be increased or decreased. From the experiment, the following results were obtained : 1. The crystallization peak temperature($T_P$) formed by apatite increased until adding up to 9wt% $TiO_2$ to base glass composition, then decreased above that. 2. Apatite($Ca_{10}P_6O_{25}$), whitlockite(${\beta}-3CaO-P_2O_5$), $\beta$-wollastonite($CaSiO_3$), magnesium tianate($MaTiO_3$) and diopside(CaO-MgO-$2SiO_2$) crystal phase were precipitated in MgO-CaO-$SiO_2-TiO_2-P_2O_5$ glass system containing 9wt% and 11wt% of $TiO_2$ 3. Vickers hardness of samples increased with increasing heat-treatment temperature and Vickers hardness of S415T9 samples heat-treated at 1075 was approxi-mately 813Kg $mm^{-2}$ as maximum value. 4. Vickers hardness of samples increased due to precipitation of apatite, whitlockite, $\beta$-wollastonite, magnesium titanate, and diopside crystal phases within glass matrix.

• 대한가정학회지
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• 제40권4호
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• pp.85-103
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• 2002

The purpose of this study is to examine determinant to purchase decisions by consumers using the home shopping of cable TV. For the purpose accomplishment, this researcher surveyed demographic characteristics of cable TV users to determine what differences in types of goods purchased by the users were made in accordance with the characteristics. Findings from the study may be reflected in bisiness policies seeking the fulfillment of consumer needs, and be used as a basic information for the establishment of consumer policies pursuing increased qualities of consumption life by providing information on goods shown through the of home shopping on cable TV. The result of the study can be summarized as follow. First, purchased goods were greatly different in their types depending on demographic characteristics of consumers such as gender, marital status, age, educational backgrounds, income and jobs. Second, experiential characteristics of cable TV users including holding or non-holding credit cards, main channels used, the main time of watching cable TV and purchase frequency per year contributed to differences in types of purchased goods. Third, factors influencing purchase decisions were somewhat different according to types of goods. However, previous purchase experiences were most influential irrespective of the types. The result as described so far suggests that previous purchase experiences by consumers raised their chances of repurchase by removing possible risks perceived by consumers. Based on the result as above, the researcher would make the following conclusion. First. companies operating the of home shopping on cable TV should increase satisfaction by consumers by providing reliable goods and information to them. In this sense, those companies need to establish marketing strategies that vary according to demographic characteristics of consumers and at the same time provide product information necessary for fulfilling consumers' requirements. Second, consumers should be moderate in the use of credit cards to avoid unplanned purchases via home shopping on cable TV and have some knowledge to solve problems related to goods and to the use of credit cards.

• 대한의용생체공학회:의공학회지
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• 제19권5호
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• pp.449-454
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• 1998

다공질 칼슘 인산계 세라믹스는 생체 친화성이 우수하여 경조직 대체재료로 사용되었을 때 새로운 인체 조직이나 실핏줄이 쉽게 성장해 들어가는 것으로 알려졌다. 본 연구에서는 여러 결정구조를 갖는 칼슘 메타인산염 중 화학적으로 가장 안정한 $\beta$형의 다공질 칼슘 메타인산염을 칼슘 인간염, Ca(H,PO,),를 열분해 시켜 제조하였다. 칼슘 인산염의 용융상태에서 냉각 중 생성되는 원통형 기공의 크기는 경조식 대체재료나 매트릭스로 사용되기 적절한 200$\mu$m로 만들기 위하여 응용온도에서 유지시간 또는 결정화 온도를 조절하였다. 본 실험에서 칼슘 인산염의 응용온도에서 유지시간을 길게 함에 따라 원통형 기공의 크기가 작아졌다.

• Journal of the Korean Wood Science and Technology
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• 제40권1호
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• pp.1-9
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• 2012

바이오매스로부터의 고밀화연료는 북미와 유럽에서 신재생에너지로서 널리 이용되고 있다. 본 연구에서는 일본잎갈나무와 현사시나무를 피스톤 프레스를 이용하여 브리켓을 제조하였으며, 연료적 특성 및 고밀화 특성을 밝히고자 압력, 가압시간, 수종 및 목분 크기가 브리켓의 특성에 미치는 영향을 조사하였다. 상온에서 110~170 MPa의 압력을 가해 제조된 일본잎갈나무와 현사시나무 브리켓의 4주간 경과 후의 밀도는 0.66~0.94 g/$cm^3$이고, 적정 가압시간은 12초이며, 제조 압력이 증가하면 브리켓의 밀도는 직선적으로 증가하였다. 일본잎갈나무 브리켓이 현사시나무 브리켓보다 밀도가 컸으며, 목분의 크기가 클수록 브리켓의 밀도가 컸다.

• 한국축산식품학회지
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• 제39권1호
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• pp.139-150
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• 2019

This study aimed to determine the suitable point of sale and consumption of different quality grade (QG) Hanwoo short loin during aging period, based on physicochemical, sensory, and microbiological quality. Short loins obtained from the carcasses of 13 Hanwoo steers and 2 bulls with 5 different QGs (1++, 1+, 1, 2, and 3) were analyzed over 28 d. QG and aging time had significant effect on water holding capacity, color, shear force, total volatile basic nitrogen (TVBN) content, and sensory traits. Higher QG groups generally exhibited a lower shear force, nucleotide content, and water holding capacity, and higher $L^*$, $a^*$, and $b^*$ values. Acceptable tenderness (shear force <5.4 kg) in QG 1++, 1+, 1, and 2 was achieved on days 7, 14, 16, and 18, respectively, and QG 3 showed a shear force of 6.8 kg, even after 28 d. Regardless of QG, TVBN content below threshold levels (20-30 mg%) was observed throughout the 28 d aging period, while total plate counts above 7 Log CFU/g were seen at 21 d. In conclusion, it is recommended that Hanwoo beef with QG 1++, 1+, and intermediate QG (1 and 2) should be sold or consumed between 7 and 21, 14 and 21, 16 and 21 d, respectively. Beef with QG 3 should be sold or consumed within 21 d, based on microbial growth, even though it has not achieved desirable tenderness. For this reason, an additional tenderizing process is recommended before this beef is ready for consumption.

• Journal of Industrial and Engineering Chemistry
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• 제67권
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• pp.358-364
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• 2018

An isotropic pitch precursor for fabricating carbon fibres was prepared by co-carbonization of ethylene bottom oil(EBO) and polyvinyl chloride (PVC). Various pre-treatments of EBO and PVC, and a high heating rate of $3^{\circ}C/min$ with no holding time, were evaluated for their effects on the oxidative stabilization process and the mechanical stability of the resulting fibres. Our stabilization process enhanced the volatilization, oxidative reaction and decomposition properties of the precursor pitch, while the addition of PVC both decreased the onset time and accelerated the oxidative reaction. Aliphatic carbon groups played a critical role in stabilization. Microstructural characterization indicated that these were first oxidised to carbon-oxygen single bonds and then converted to carbon-oxygen double bonds. Due to the higher heating rate and lack of a holding step during processing,the resulting thermoplastic fibers did not completely convert to thermoset materials, allowing partially melted, adjacent fibres to fuse. Fiber surfaces were smooth and homogeneous. Of the various methods evaluated herein, carbon fibers derived from pressure-treated EBO and PVC exhibited the highest tensile strength. This work shows that enhancing the naphthenic component of a pitch precursor through the co-carbonization of pre-treated EBO with PVC improves the oxidative properties of the resulting carbon fibers.

• 대한금속재료학회지
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• 제50권4호
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• pp.271-279
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• 2012

9-12% Cr steels have been used in thermal power plants which repeat start and stop operations. Major factors of fatigue life are temperature, frequency, stress ratio, holding time, microstructure, and environment. Normally, fatigue life decreases at high temperature, low frequency, high stress ratio, and long holding time conditions. A Mod.9Cr-1Mo steel, called G91, was developed at ORNL (Oak Ridge National Laboratory, USA) and was adopted as a high-temperature structural material in the ASME Code in 2004. However, its low-cycle fatigue and fatigue crack growth characteristics have been rarely studied. In this work, we have investigated the low-cycle fatigue crack growth behaviors of G91 steel under various test conditions in terms of temperature and stress ratio. As temperature and stress ratio increase, the crack growth rate becomes faster and striation distance also increases. On the other hand, the number of branch cracks decreases.

• Design & Manufacturing
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• 제17권3호
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• pp.8-14
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• 2023

In this study, basic research was conducted on manufacturing technology of thick-walled light guide a component that controls the light source of automobile lamps. As a preliminary study for manufacturing the final injection molded parts, a model for analyzing the influence of micro patterns on light guides is presented. The optical characteristics of the light guide were analyzed according to the change of the curvature radius of the micro-optical pattern, and the injection molding characteristics of the light guide according to the change of injection molding conditions were analytically evaluated. It was confirmed that the luminance uniformity improves as the R value decreases for changes in the micro-pattern R value, but it was confirmed that there are technical limitations in actual injection mold core processing and high-replication injection molding. Injection molding analysis showed that cooling channel design is very important compared to general injection molding due to thick-wall characteristics and thickness variation. It was also confirmed that the cooling channel has a great influence on the cycle time and birefringence result due to residual stress. As a result of analyzing the influence of filling time, holding condition, and cooling on shrinkage, it was found that the cooling water temperature has a significant effect on the shrinkage of ultra-fine light guide parts, and the holding condition also has a significant effect.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제18권5호
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• pp.1390-1411
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• 2024

Underwater Wireless Sensors Networks (UWSNs) are deployed in remotely monitored environment such as water level monitoring, ocean current identification, oil detection, habitat monitoring and numerous military applications. Providing scalable and efficient routing is very challenging in UWSNs due to the harsh underwater environment. The biggest difficulties are the nodes inherent movement due to water current, long delay in data transmission, low bandwidth of the acoustic signal, high error rate and energy scarcity in battery powered nodes. Many routing protocols have been proposed to solve the aforementioned problems. There are three broad categories of routing protocols namely depth based, energy based and vector-based routing. Vector Based Forwarding protocols perform routing through virtual pipeline by defining their radius which give proper direction to packets communication. We proposed a routing protocol termed as Path-Oriented Energy Scaled Expanded Vector Based Forwarding (PESEVBF). PESEVBF takes into account all parameters; holding time, the source nodes packets routing path and void holes creation on the second hop; PESEVBF not only considers the packet upward advancement but also focus on density of the forwarded nodes in terms of number of potential forwarding and suppressed nodes for path selection. Node selection in resultant holding time is based on minimum Path Factor (PF) value. Moreover, the suppressed node will be selected for packet forwarding to avoid the void holes occurrences on the second hop. Performance of PESEVBF is compared with other routing protocols using matrices such as energy consumption, packet delivery ratio, packets dropping ratio and duplicate packets creation indicating considerable performance improvement.

• 한국통신학회논문지
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• 제30권9A호
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• pp.737-748
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• 2005

본 연구에서는 직접 대역확산 부호분할 시스템에서 음성 및 흐름형 데이터의 통합 서비스를 위한 두 가지 유연한 호 수락제어 방식을 제안한다. 호 수락제어에 대한 기존 연구는 대부분 종래의 음성 서비스와 짧고 버스티한 특성의 패킷 형 서비스와의 통합 서비스에 관점을 두었다. 하지만 상대적으로 긴 서비스 유지 시간을 갖는 흐름형 서비스는 차세대 이동통신 시스템에서 데이터 트래픽의 상당한 부분을 차지할 것으로 예상된다. 제안된첫 번째 방식. 방식 I은 음성과 흐름형 데이터 서비스를 수용하기 위하여 주어진 대역을 모두 사용하는 기본 방식이며 데이터 서비스에 대하여 음성 서비스가 우선권을 갖는다. 두 번째 방식, 방식 II는 흐름형 데이터 서비스에 대하여 음성에 우선권을 주면서 대역을 효율적으로 사용하기 위해서 다른 방식을 취한다. 음성 서비스의 접근 요구와 간섭의 상태에 따라서 흐름형 데이터 서비스의 사용 전력을 억제하여 추가적인 간섭 마진을 음성 서비스에 제공한다. 이 두 방식의 성능은 마코비안 모델을 통하여 분석하였고 그 수치적인 결과는 음성 용량은 데이터 서비스의 서비스 유지 시간에 매우 민감한 반면 데이터 용량은 둔감하였다. 음성 및 흐름형 데이터 서비스의 통합 환경에서 두 번째 제안 방식이 첫 번째 방식보다 시스템 용량 상에 상당한 개선 효과를 갖는 것으로 나타난다.