• Journal of Communications and Networks
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• 제16권6호
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• pp.656-666
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• 2014

In delay tolerant networks (DTNs), delay is inevitable; thus, making better use of buffer space to maximize the packet delivery rate is more important than delay reduction. In DTNs, epidemic routing is a well-known routing protocol. However, epidemic routing is very sensitive to buffer size. Once the buffer size in nodes is insufficient, the performance of epidemic routing will be drastically reduced. In this paper, we propose a buffer scheme to optimize the performance of epidemic routing on the basis of the Lagrangian and dual problem models. By using the proposed optimal buffer scheme, the packet delivery rate in epidemic routing is considerably improved. Our simulation results show that epidemic routing with the proposed optimal buffer scheme outperforms the original epidemic routing in terms of packet delivery rate and average end-to-end delay. It is worth noting that the improved epidemic routing needs much less buffer size compared to that of the original epidemic routing for ensuring the same packet delivery rate. In particular, even though the buffer size is very small (e.g., 50), the packet delivery rate in epidemic routing with the proposed optimal buffer scheme is still 95.8%, which can satisfy general communication demand.

• 대한기계학회논문집A
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• 제25권12호
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• pp.1933-1943
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• 2001

A micromechanical model is presented for superplasticity in which heterogeneous microstructures are coupled with deformation behavior. The effects of initial distributions of grain size, and their evolutions on the mechanical properties can be predicted by the model. Alternative stress rate models such as Jaumann rate and rotation incremental rate have been employed to analyze uniaxial loading and simple shear problems and the appropriate modeling was studied on the basis of hypoelasticity and elasto-viscoplasticity. The model has been implemented into finite element software so that full process simulation can be carried out. Tests have been conducted on Ti-6Al-4V alloy and the microstructural features such as grain size, distributions of grain size, and volume fraction of each phase were examined for the materials that were tested at different strain rates. The experimentally observed stress-strain behavior on a range of initial grain size distributions has been shown to be correctly predicted. In addition, the effect of volume fraction of the phases and concurrent grain growth were analyzed. The dependence of failure strain on strain rate has been explained in terms of the change in mechanism of grain growth that occurs with changing strain rate.

• 한국환경보건학회지
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• 제47권2호
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• pp.175-181
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• 2021

Objectives: The correlation between the size of a leak hole, the volume of the leakage, and the range of influence was investigated for a hydrochloric acid tank-lorry. Methods: For the case of a tank-lorry chemical accident, KORA (Korea Off-site Risk Assessment Supporting Tool) was used to predict the leak rate and the range of influence according to the size of the leak hole. The correlation was studied using R. Results: As a result of analyzing the leak rate change according to the leak hole size in a 35% hydrochloric acid tank-lorry, as the size of the leak hole increased from 1 to 100 mm, the leak rate increased from 0.008 to 83.94 kg/sec, following the power function. As a result of calculating the range of influence under conditions ranging from 1 to 100 mm in size and 10 to 60 minutes of leakage time, it was found that the range spanned from a minimum of 5.4 m to a maximum of 307.9 m. As a result of multiple regression analysis using R, the quadratic function model best explained the correlation between the size of the leak hole, the leak time, and the range of influence with an adjected coefficient of determination of 0.97 and a root mean square error of 22.33. Conclusion: If a correlation database for the size of a leak hole is accumulated for various substances and under various conditions, the amount of leakage and the range of influence can easily be calculated, facilitating field response activities.

• 한국콘텐츠학회논문지
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• 제18권4호
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• pp.416-427
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• 2018

부동산PF는 대출의 상대적 규모가 커서 연체가 발생되면 시장의 파급력도 커진다. 따라서 부동산PF 연체율에 대한 관리와 거시경제적 분석이 필요하다. 선행연구에서는 주로 개별 은행의 부동산PF 데이터를 통한 미시적인 분석을 진행하여 리스트의 중요성을 평가하거나, 연체에 대한 결정요인을 분석하여 전체적인 부동산PF 규모에 의한 연구가 미흡하였다. 본 연구는 이러한 자료의 한계점을 극복하고자 거시경제변수에 따른 시장전체의 부동산PF 연체율에 대한 영향관계를 연구하였다. 본 연구는 부동산PF 대출규모, 통화량, 금리, 소비자물가지수, GDP 자료를 활용하였으며, 공적분검정 결과 적어도 2개 변수 이상에서 선형관계가 이루어짐에 따라 VECM의 1차 모형을 적용하였다. 그랜저인과관계 결과 부동산PF 연체율은 부동산PF 대출금액에 영향을 받으며, 충격반응결과 통화량, 소비자 물가지수, 금리, 대출금액, GDP 순으로 연체율에 큰 영향을 주는 것으로 나타났다. 향후 부동산PF 자금 대출 이후 금리 상승은 부동산PF 연체율에 부담을 주게 되며, 통화량의 증가는 물가의 상승을 유도하여 결국 금리상승으로 이어질 수 있어 대출규모가 클수록 위험성의 노출이 심각해 질 수 있다. 따라서 부동산PF 연체율의 관리는 대출 이후 거시적 관점에서 자금 회수에 지속적 추적과 관찰이 필요하며, 이를 통해 연체율 방지를 위한 관리방안이 필요할 것이다.

• Bulletin of the Korean Chemical Society
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• 제30권7호
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• pp.1598-1602
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• 2009

The particle size of Li[$Ni_{0.2}Li_{0.2}Mn_{0.6}]O_2$ cathode powder was controlled effectively by dispersion using lauric acid as a surfactant. The samples treated by lauric acid showed smaller particles of approximately half the original size compared to the particles of a pristine sample. A structural change due to the dispersion of Li[$Ni_{0.2}Li_{0.2}Mn_{0.6}]O_2$ powder was not detected. The rate performance of the Li[$Ni_{0.2}Li_{0.2}Mn_{0.6}]O_2$ cathode was improved by dispersion using lauric acid, which was likely due to the decrease of the particle size. In particular, a sample dispersed pristine powder using lauric acid (L2) presented a greatly enhanced discharge capacity and capacity retention at a high C rate. The discharge capacity of a pristine sample was only 133 m$Ahg^{-1}$ (3C rate) and 96 m$Ahg^{-1}$ (12C rate) at the tenth cycle. In contrast, the L2 electrode delivered higher discharge capacities of 160 m$Ahg^{-1}$ (3C rate) and 129 m$Ahg^{-1}$ (12C rate) at the tenth cycle. The capacity retention at a rate of 12C/2C was also enhanced from ~ 45% (pristine sample) to 57% (L2) by treatment with lauric acid.

• 한국의류학회지
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• 제40권5호
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• pp.954-965
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• 2016

This study was designed to help develop an optimized sizing system for the military winter jackets of Korean males. First, we conducted a survey on the supply rate of military winter jackets and the wearing of suitable size jackets in order to identify problems in the current sizing system. We next developed a new sizing system generation method to satisfy the coverage rate and appropriate size number: Hybrid of Grid with Optimization. The findings of this study were: 1. The survey indicated that a 90 (chest girth) size is necessary; in addition, a one-step large size jacket fit well as a right size jacket. 2. We developed three optimized sizing systems for Korean male military winter jackets using the Hybrid of Grid with an optimization method and suggested one of them as a final new sizing system. The new sizing system consisted of two primary dimension: chest girth and stature. It has a 14 size number and its extended coverage rate is larger than the current sizing system and it has a 90 (chest girth) size. It also selected an optimized size for the area of low population density. The new sizing system is therefore considered very effective for Korean male soldiers military winter jackets.

• 대한기계학회논문집
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• 제11권6호
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• pp.867-876
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• 1987

본 연구에서는 보통강재인 SS 41 강을 열처리하여 얻은 M.E.F.복합조직강의 모상입경변화와 3.5% NaCl수용액의 pH변화 조건하에서 반복굽힘피로실험을 하여 부식 피로파괴에 미치는 영향에 대해 고찰하였다.

• 한국분말재료학회지
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• 제17권5호
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• pp.379-384
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• 2010

In the present work, bismuth nanopowders with various particle size distributions were synthesized by controlling argon (Ar) gas flow rate and chamber pressure of a gas condensation (GC) apparatus. From the analyses of transmission electron microscopy (TEM) images and nitrogen gas adsorption results, it was found that as Ar gas flow rate increased, the specific surface area of bismuth increased and the average particles size decreased. On the other hand, as the chamber pressure increased, the specific surface area of bismuth decreased and the average particles size increased. The optimum gas flow rate and chamber pressure for the maximized electrochemical active surface area were determined to be 8 L/min and 50 torr, respectively. The bismuth nanopowders synthesized at the above condition exhibit 13.47 $m^2g^{-1}$ of specific surface area and 45.6 nm of average particles diameter.

• 한국결정성장학회지
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• 제15권1호
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• pp.34-38
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• 2005

Langasite 단결정 wafer의 chemical mechanical planarization 공정에서 pH level 및 slurry 입도가 가공속도 및 평탄화도에 미치는 영향을 조사하였다. 낮은 pH level 조건하에서 더 높은 가공속도 값이 얻어진 반면에 평탄화도는 colloidal silica slurry의 평균입경에 의해 좌우됨을 확인하였다. 0.045 ㎛의 비정질 silica 입자를 함유한 슬러리를 사용하였을 때 표면에 잔류 scratch 형성이 없이 가장 좋은 가공성을 확보할 수 있었다. 가공속도와 평탄화도는 effective particle number에 대한 강한 의존성을 나타내었으며, effective particle number가 낮은 조건하에서 가공속도는 더 낮은 분포를 나타내었으나 평탄화도는 더 우수한 경향성을 확인하였다.

• 대한영양사협회학술지
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• 제4권2호
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• pp.132-144
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• 1998

The purpose of this study is setting proper portion by consumed size of food and food preference and then reducing plate wasts in school lunch. The survey was conducted from Oct. 21 to Nov. 22, 1996 through the practical measurement and questionnaires. The subjects were 43 students of 1 elementary school. The results of this survey was as follows : 1. Average consumption size of cooked rice was 115g. Average consumption size of one course dishes was 209g. The soup & pot stewes showed lower consumption rate than the other kind of foods. Average consumption size of fresh & boiled salad was 23.4g Average consumption size of stir fries was 55g. Average consumption size of steams & stewes was 42g. Most grill & fried foods showed high consumption rate compared to most of the other foods. Average consumption size of kimchies was 10.6g. The most of given desserts except apple were all consumed. 2. There was significant correlation between food preference and consumption rate for total food items. 3. Response of satisfaction about serving size of most of given foods except fresh & boiled salads, soup & pot stewes and kimchies were "moderate". 4. Visual estimation was greater than physical estimation for most of given foods. Proper portion of foods per person by results were setted as follows :