목적: 본 연구에서는 근시도에 따라 나누어 동공크기에 의한 굴절이상도의 차이에 영향을 미치는 요인을 알아보고자 하였다. 방법 : 안경원을 방문하여 i.profilerplus(Zeiss, Berlin, Germany) 검사를 시행 받은 18~56세의 성인 73명 (73안)을 대상으로 하였다. 대상자를 경도 근시, 중등도 근시, 그리고 고도 근시로 분류하였다. 각 근시 그룹에서 동공크기(5, 3 mm)에 따른 구면렌즈 대응치의 차이를 비교하였다. Multiple regression analysis를 시행하여 각 근시 그룹에서 동공크기에 따른 평균 구면렌즈 대응치의 차이에 영향을 미치는 인자를 평가하였다. 결과 : 평균 구면렌즈 대응치는 5 mm에 비해 3 mm일 때 경도 근시(–1.99±0.76 D와 -1.68±0.72 D), 중등도 근시(–4.24±0.97 D와 -4.04±0.90 D), 그리고 고도 근시(-8.06±1.51 D와 -7.95±1.40 D) 모두 유의하게 낮았다. 경도와 고도 근시에서는 구면수차와 수직코마수차가 동공크기에 따른 평균 구면렌즈 대응치의 차이에 영향을 미쳤으며, 중등도 근시에서는 구면수차가 동공크기에 따른 평균 구면렌즈 대응치의 차이에 영향을 미치는 것으로 나타났다. 결론 : 근시도에 따라 동공크기가 변화할 경우 고위수차가 영향을 미치는 것으로 나타났으며, 안경사는 근시안의 경우 야간시에서 흐린 이미지로 인한 불편함의 가능성이 있음을 이해하고 안경처방을 해야 할 것으로 생각한다.

In general, small and medium-sized computer rooms do not have access floors for reasons of increased floor height and increased construction cost. Therefore, the air conditioning method used here applies the method of directly blowing the cold air of the air conditioner into the computer room. In this case, the hot/cold air is not separated, and as the hot air is recirculated, it is re-introduced to the front of the server rack, resulting in a problem that the server cooling efficiency is decreased. In addition, in such a computer room structure, it is difficult to configure and install a containment system. In this study, we tried to understand the problem of the formation airflow in the case of using the existing air conditioning method, and to find a method of configuring the air conditioning environment to improve the cooling efficiency. The purpose of this study was to understand the airflow/temperature distribution in the computer room using the CFD simulation method. In addition, the thermal characteristics of various air-conditioning environments such as the location of the CRAC cold air discharge location, the layout between server rack and CRAC and the containment were reviewed.

This study was conducted to provide basic data for evolving a strategy for the development of Vietnam’s customized HMR program and formulating a marketing strategy by analyzing the characteristics and variations of HMR consumption behavior by household size. The results of the analysis were as follows: The number of single households using HMR as a general meal at home was higher than multiple-person households. Moreover, there was a high preference for ‘ready to heat’ and ‘ready to eat’ products, which are relatively easy to cook and prepare. It was observed that single households preferred department stores, hypermarkets, and convenience stores for purchasing HMR when compared to multiple households, and that single households preferred to acquire information through TV/radio and internet advertisements. Among the HMR selection attributes, single households valued taste, quantity, price, preparation process, preparation time, and ease of storage as important. Reflecting on the results of this study, when developing HMR in Vietnam, it is necessary to develop a product that can nutritionally replace the general meal with a focus on convenience. In addition, there is a need for products that possess various attributes such as convenience, health, and eco-friendliness.

Multi-walled carbon nanotubes (MWCNTs) grown by chemical vapor deposition retain the residual catalyst particles from which the growth occurred, which are considered a detriment to MWCNTs’ performance, especially electrical conductivity. The first direct measurements have been made of the electrical transport through the catalyst cap into the MWCNT using nanoscale 2-point-probe to determine the effects of the catalyst particle’s size and the diameter ratio with its associated MWCNT on the electrical transport through the catalyst cap as compared to the inherent conductivity of the MWCNT. The MWCNT diameter is independent of the catalyst size, but the ratio of the catalyst cap diameter to MWCNT diameter (DC/DNT) determines the conduction mechanism. Where DC/DNT is greater than 1 the resulting I–V curve is near ohmic, and the conduction through the catalyst ( RC+NT) approaches that of the MWCNT (RNT); however, when the DC/DNT < 1 the I–V curves shift to rectifying and RC+NT > > RNT. The experimental results are discussed in relation to current crowding at the interface between catalyst and nanotube due to an increased electric field.

This study examined the effects of micro- (crystallinity) and macro (orientation)-crystalline properties of graphite on the initial efficiency, discharge capacity, and rate performance of anodic materials. Needle coke and regular coke were selected as raw materials and pulverized to 2–25 μm to determine the effects of crystalline properties on particle shape after pulverization. Needle coke with outstanding crystallinity had high initial efficiency, and smaller particles with larger specific surface areas saw increased irreversible capacity due to the formation of SEI layers. Because of cavities existing between crystals, the poorer the crystalline properties were, the greater the capacity of the lithium ions increased. As such, regular coke had a 30 mAh/g higher discharge capacity than that of needle coke. Rate performance was more affected by particle size than by crystalline structure, and was the highest at a particle distribution of 10–15 μm.

본 연구는 6개 핵돈군생산농장(Great grand parents, GGP)에서 2015년 이후 태어난 Landrace종과 Yorkshire종의 두 품종에 대하여 생시체중 (Birth weight; BW), 복당평균생시체중(Mean of litter birth weight; MBW0)과 변이계수(Coefficient of variation in MBW0; CVMBW0) 및 산자수(Litter size) 등에 대한 유전모수를 추정하였다. Landrace종에서 총산자수(Total number of piglets born; TNB), 생존산자수(Number of piglets born alive: NBA), 복당평균생시체중 및 복당평균생시체중 변이계수의 유전력은 각각 0.14, 0.09, 0.33 및 0.16. Yorkshire종에서는 각각 0.11, 0.99, 0.28 및 0.07로 추정되었다. 산자수와 복당평균생시체중 간에는 부(-)의 상관관계를 나타내었으며, 복당평균생시체중과 변이계수사이의 표현형상관과 유전상관이 두 품종에서 모두 –0.40에서 –0.45로 높게 나타났다. 자돈 생시체중에 대한 균일도를 개량하기 위해서는 복당평균생시 체중(MBW0)과 복당평균생시체중변이계수(CVMBW0)를 선발지수식에 포함시키는 것이 바람직하다고 생각된다.

High-strength low-alloy (HSLA) steels show excellent toughness when trace amounts of transition elements are added. In steels, prior austenite grain size (PAGS), which is often determined by the number of added elements, is a critical factor in determining the mechanical properties of the material. In this study, we used two etching methods to measure and compare the PAGS of specimens with bainitic HSLA steels having different Nb contents These two methods were nital etching and picric acid etching. Both methods confirmed that the sample with high Nb content exhibited smaller PAGS than its low Nb counterpart because of Nb’s ability to hinder austenite recrystallization at high temperatures. Although both etching approaches are beneficial to PAGS estimation, the picric acid etching method has the advantage of enabling observation of the interface containing Nb precipitate. By contrast, the nital etching method has the advantage of a very short etching time (5 s) in determining the PAGS, with the picric acid etching method being considerably longer (5 h).

This study was conducted to evaluate the performance of the octopus pot according to mesh sizes. Entering behavior of Octopus minor and bait (Macrophthalmus japonicus) escape rate on the mesh sizes of the pots were investigated for six times in indoor tank. The sea trials for evaluating the performance of Octopus minor pot to different mesh sizes (22, 20 and 18 mm) were conducted for six times from 2017 to 2018 in the coastal sea of Deukyang Bay, the Republic of Korea. Behavior patterns of contact pot to leaved pot were more frequent than contact pot to bait search. When the octopus contacted to the pot, there was no clear search behavior to distinguish the mesh sizes. Total catch of 46% was accounted for 18 mm pots, followed by 34% at 20 mm and 20% at 22 mm (P < 0.05). Catch per unit effort was calculated as 30 g/pot at 22 mm, 44 g/pot at 20 mm and 59 g/pot at 18 mm. As a result of evaluating 50% selection of mantle length and weight on the mesh sizes, mantle length (mm) and weight (g) were 84.6 and 147.8 in 22 mm, followed by 20 and 18 mm.

Understanding of effects of changes in the particle size of the matrix material on the mullite whisker growth during the production of porous mullite is crucial for better design of new porous ceramics materials in different applications. Commercially, raw materials such as Al2O3/SiO2 and Al(OH)3/SiO2 are used as starting materials, while AlF3 is added to fabricate porous mullite through reaction sintering process. When Al2O3 is used as a starting material, a porous microstructure can be identified, but a more developed needle shaped microstructure is identified in the specimen using Al(OH)3, which has excellent reactivity. The specimen using Al2O3/SiO2 composite powder does not undergo mulliteization even at 1,400 oC, but the specimen using the Al(OH)3/SiO2 composite powder had already formed complete mullite whiskers from the particle size specimen milled for 3 h at 1,100 oC. As a result, the change in sintering temperature does not significantly affect formation of microstructures. As the particle size of the matrix materials, Al2O3 and Al(OH)3, decreases, the porosity tends to decrease. In the case of the Al(OH)3/SiO2 composite powder, the highest porosity obtained is 75% when the particle size passes through a milling time of 3 h. The smaller the particle size of Al(OH)3 is and the more the long/short ratio of the mullite whisker phase decreases, the higher the density becomes.

목적 : 근시안에서 조도에 의한 동공크기와 동공중심이탈에 따른 고위수차의 변화를 확인하고자 하였다. 방법 : 각막굴절교정수술의 경험이 없고 안질환이 없는 건강한 성인 33명(평균 연령: 23.03±2.8세, 평균 등 가구면굴절력: -3.28±1.67 D, 66안)을 대상으로 하였다. 동공크기, 동공중심이탈(pupil center off-set), 고위 수차는 Wavefront Analyzer를 사용하여 기기에서 조정되는 암소시(scotopic, 0 lx)와 명소시(photopic, 20 lx)상태에서 3회 측정하고 평균값을 사용하였다. 통계분석은 SPSS(version 21.0)을 사용하였다. 결과 : 명소시 상태에서 동공크기는 암소시 상태보다 2.00 mm 감소하고(p<0.001) 근시안의 굴절이상도와 관련이 있었으며, 동공중심 offset은 0.09 mm 증가하고(p<0.003) 굴절이상도와는 관련이 없었다. 또한 동공중심 이동량은 0.17±0.13 mm로 주로 상이측, 상비측 방향으로 이동하였다. 전체 고위수차는 동공크기와 동공중심 offset 모두에서 상관성이 없었고, 구면수차는 동공크기와 상관성이 있었으며(p=0.006, p=0.007). 코마수차는 동공중심 offset과 상관성이 있었다(p=0.027, p=0,008). 결론 : 동공크기는 구면수차와 동공중심 offset은 코마수차와 상관성이 있어 조도에 따라 동공크기와 동공중심 offset이 변하면, 시력의 질에 영향을 미칠 것으로 사료된다.

PURPOSES : The exposed aggregate number (EAN) and mean texture depth (MTD) of exposed aggregate concrete pavement (EACP) influence the functional performance of EACP in terms of pavement noise and skid resistance. The selection of the exposure time of EACP is important because the designed EAN and MTD of EACP can be achieved when the exposure process is performed at an appropriate time. On the one hand, too early exposure may cause protrusions and unwanted removal of aggregates and mortar. On the other hand, late exposure may cause difficulty in exposure of the mortar. In this study, a method to determine the optimum exposure time for EACP is suggested using a non-destructive method. METHODS : A set of laboratory tests was performed to investigate the variation in EAN and MTD of EACP according to the elastic modulus obtained by non-destructive equipment. From the results of this investigation, the optimum exposure time using the non-destructive method and the exposure time window (ETW) method was suggested. In addition, the usefulness of ETW suggested by laboratory tests was verified from a field application. RESULTS : From the laboratory tests, it was found that the targets of the surface condition of EACP (EAN: 59 per 25 cm2, MTD: 1.39 mm) can be achieved when the concrete elastic modulus is higher than 20GPa. The proposed guideline using the non-destructive method was applied for the field construction of EACP and achieved similar results. CONCLUSIONS : It was found that the proposed guideline for determining the exposure time window based on non-destructive testing is useful.

In defense acquisition system, testing and evaluation is a very important procedure that can ensure the completeness of capability while deciding whether to mass-produce or purchase weapons systems. But it always includes realistic restrictions that involve a variety of stakeholders, but lack of time, resources, and budget. Therefore, in the process of planning a test and evaluation, proper number of prototypes and reliability of test results, along with test items and evaluation criteria, are frequently discussed as sensitive agendas. In reality, however, rather than statistical judgments, the number of prototypes and tests are determined by business logic such as duration and budget. Otherwise, most theoretical studies do not adequately reflect the business logic of test assessment. In this study, we propose a number of prototype and tests method that can statistically reasonably verify the performance of the inorganic system considering the characteristics of each test and evaluation project. To this end, we consider the theory related to determining the number of prototypes and tests, and present examples by separating whether to secure the magnitude of effects that have a significant impact on statistical judgment. This study could contribute to the development of empirical methodologies that can adequately coordinate reality and theory in the field of defense test evaluation while ensuring statistical reliability of test evaluation results.