This study was conducted to help manage total floating bacteria and fungi in the indoor air by studying the characteristics of total floating bacteria and fungi according to the indoor CO2 concentration of daycare centers. The sampling and analysis of samples was based on the indoor air quality process test method, and the result analysis was conducted using the SPSS statistical program to perform correlation and regression analysis. Correlation and regression results show that CO2 and total airborne bacteria showed positive relationships, but airborne mold did not show relevance. In addition, in order to identify factors affecting airborne mold, correlation analysis and regression analysis were performed regarding total airborne bacteria, PM10, PM2.5, HCHO, outdoor mold, I/O ratio, indoor temperature/ humidity, area per classroom and volume. The results showed that the factors affecting airborne mold were I/O ratio, outdoor airborne mold, and total airborne bacteria. Research results show that CO2 and total airborne bacteria can be reduced and controlled by natural ventilation, and in the case of airborne mold, mechanical forced ventilation such as hoods will be necessary due to the introduction of outdoor airborne mold. In addition, it is necessary to consider I/O ratio criteria in order to confirm effective indoor mold contamination, taking into account the effect of outdoor mold inflow.

연구목적 : 본 연구는 착석시 의자등받이가 사용자의 허리를 감싸안고 척추형태에 반응하여 자연스러운 척추 곡선을 유지 및 증진시켜 줌으로써 바른 자세 유지 및 허리 피로감 해소에 도움을 주는 척추 굴곡 반응형 의자등받이를 개발하고 이의 효과를 과학적으로 검증하는데 목적을 두었다. 연구방법 : 척추 굴곡 반응형 등받이는 일반 사무용 의자에 탈부착이 가능하며 사용자가 허리를 기댔을 때 등받이가 사용자의 척추라인에 따라 반응하도록 하여 허리 전체가 등받이에 밀착됨으로써 척추의 자연스러운 굴곡 형태를 유지하고 증진시키도록 개발하였다. 개발된 등받이의 효과성 검증을 위해 표준체형의 남자대학(원)생 10명을 피실험자로 선정하여 동작분석기와 근전계를 활용하여 착석시 척추 굴곡의 변화 측정과 척추 세움근의 활성도를 측정하였다. 결과 : 개발된 등받이와 비교 대상 의자에 착석시 척추 곡선 변화에 대한 동작분석기 평가결과, 등받이 각도 105o부터 시작하여 리클라이닝 각도가 125o로 커짐에 따라 요추의 전만곡과 흉추의 후만곡이 커짐으로써 척추 곡선이 증진됨을 보였다. 근전계를 활용한 척추 세움근(L5/S1)의 평가결과 개발된 의자를 사용했을 때 모든 등받이 각도에서 사후 중앙주파수 값이 사전 중앙주파수 값보다 높게 측정됨으로써 피 로지수가 낮아졌음을 알 수 있었다. 결론 : 본 연구에서 개발한 척추 굴곡 반응형 등받이는 착석시 바른자세를 유지하게 하여 허리근육의 긴장완화와 허리디스크에 가해지는 압력을 감소시켜 장시간 앉아서 업무를 보거나 공부하는 학생들의 피로감을 줄여줄 의자로써 활용이 가능하며 향후 이의 도입과 확산을 위한 추가적인 연구개발의 필요성을 제안한다.

In this study, a nanocrystalline FeNiCrMoMnSiC alloy was fabricated, and its austenite stability, microstructure, and mechanical properties were investigated. A sintered FeNiCrMoMnSiC alloy sample with nanosized crystal was obtained by high-energy ball milling and spark plasma sintering. The sintering behavior was investigated by measuring the displacement according to the temperature of the sintered body. Through microstructural analysis, it was confirmed that a compact sintered body with few pores was produced, and cementite was formed. The stability of the austenite phase in the sintered samples was evaluated by X-ray diffraction analysis and electron backscatter diffraction. Results revealed a measured value of 51.6% and that the alloy had seven times more austenite stability than AISI 4340 wrought steel. The hardness of the sintered alloy was 60.4 HRC, which was up to 2.4 times higher than that of wrought steel.

연층을 가지는 건축물들의 피해사례가 관측됨에 따라 기존 건축물 내진성능평가시 수직비정형의 고려가 중요해졌다. 하지만 기존 방법은 수직비정형을 충분히 반영하기 어렵기 때문에 수직비정형을 가지는 건축물에 대해 내진성능을 과소 혹은 과대평가할 여지가 있다. 본 연구는 강성기반 연층비(Soft Story Ratio, SSR)를 이용해 수직비정형 건축물의 내진성능평가 기법을 개발하는데 목적이 있다. SSR은 변위에 대한 요구량과 능력의 비율을 나타내고, 강성차이에 의한 수직비정형을 고려하여 건축물의 변위집중 비율을 의미하는 파라미터다. 1층 기둥을 변수로 하는 필로티 건축물 네 개를 대상으로 개발한 내진성능평가 기법을 기존의 내진성능평가 기법과 비교하였다. 기존 기법은 수직비정형이 극대화되는 모델에 대해 내진성능을 과대평가하는 경우가 발생하였다. 반면 제안된 기법은 모든 모델에 대해서 상세평가의 결과와 동일했다. 따라서 제안하는 내진성능평가 기법은 수직비정형이 극대화되는 필로티 건축물에서 기존의 방법보다 정밀하게 내진성능평가 결과를 제공할 수 있다고 사료된다.

PURPOSES : The Korea Expressway Corporation has been working on an early remodeling project for the Jungbu Expressway, to prepare techniques for the rehabilitation of the old CRCP. In this study, a literature review, field survey, and thickness design using MEPGD were conducted. This is to provide a procedure for the pre-treatment, or repair of the existing pavement in the JungBu Expressway. METHODS : To evaluate the pavement condition of the JungBu Expressway, the existing PMS data were analyzed, and field surveys were conducted for each pavement condition. The SMA overlay thickness design was performed using the pavement thickness design program (MEPGD). In addition, the repair procedure was reviewed considering the characteristics of the old CRCP in Korea. RESULTS : From the analysis of existing PMS, field surveys, and laboratory tests, it was discovered that the old CRCP condition of the Jungbu Expressway was not satisfactory. Using MEPDG, the SMA thicknesses for each scenario were proposed as 5, 8, and 10 cm. In addition, appropriate repair procedures for each distress type(punchpout, multiple repair, re-failure, failure of longitudinal joint, etc.) of damaged CRCP in Korea were proposed. CONCLUSIONS : For the remodeling project of the Jungbu Expressway, appropriate repairs should be performed for each type of distress in the old CRCP. In this study, an appropriate overlay thickness and pre-treatment method are suggested.

The effect of sintering conditions on the austenite stability and strain-induced martensitic transformation of nanocrystalline FeCrC alloy is investigated. Nanocrystalline FeCrC alloys are successfully fabricated by spark plasma sintering with an extremely short densification time to obtain the theoretical density value and prevent grain growth. The nanocrystallite size in the sintered alloys contributes to increased austenite stability. The phase fraction of the FeCrC sintered alloy before and after deformation according to the sintering holding time is measured using X-ray diffraction and electron backscatter diffraction analysis. During compressive deformation, the volume fraction of strain-induced martensite resulting from austenite decomposition is increased. The transformation kinetics of the strain-induced martensite is evaluated using an empirical equation considering the austenite stability factor. The hardness of the S0W and S10W samples increase to 62.4-67.5 and 58.9-63.4 HRC before and after deformation. The hardness results confirmed that the mechanical properties are improved owing to the effects of grain refinement and strain-induced martensitic transformation in the nanocrystalline FeCrC alloy.

We fabricate the non-equiatomic high-entropy alloy (NE-HEA) Fe49.5Mn30Co10Cr10C0.5 (at.%) using spark plasma sintering under various sintering conditions. Each elemental pure powder is milled by high-energy ball milling to prepare NE-HEA powder. The microstructure and mechanical properties of the sintered samples are investigated using various methods. We use the X-ray diffraction (XRD) method to investigate the microstructural characteristics. Quantitative phase analysis is performed by direct comparison of the XRD results. A tensile test is used to compare the mechanical properties of small samples. Next, electron backscatter diffraction analysis is performed to analyze the phase fraction, and the results are compared to those of XRD analysis. By combining different sintering durations and temperature conditions, we attempt to identify suitable spark plasma sintering conditions that yield mechanical properties comparable with previously reported values. The samples sintered at 900 and 1000oC with no holding time have a tensile strength of over 1000 MPa.

췌장고형종양의 초음파 내시경(endoscopic ultrasound, EUS) 유도하 조직 검사는 기술적 난이도가 높고 침습적이기 때문에 임상에서의 적절한 사용을 위해 엄격한 권고안을 필요로 한다. 이에 대한소화기내시경학회에서는 췌장고형종양의 초음파 내시경 유도하 조직 검사를 위한 임상진료지침을 개발하기 위해 진료지침 개발위원회를 발족하였다. 권고안의 등급과 개별 권고안의 근거 수준은 2014년 출판된 임상진료지침 개발을 위한 Minds Handbook에서 제시된 체계에 기반하여 평가하였다. 본 진료지침 개발위원회는 초음파 내시경 분야의 전문가 16인과 임상진료지침 개발방법론 전문가 1인으로 구성되었으며, 8개 분야에 걸쳐 총 12건의 근거 기반 권고안을 개발하여 췌장고형종양 진단 시 임상의들이 근거에 기반한 임상적 판단을 할 수 있도록 돕고자 하였다. 본 임상 진료지침은 췌장고형종양에서 초음파 내시경 유도하 조직 검사에 대해 다루고 있으며, 권고안에서는 해당 검사의 적응증, 진단 정확도를 최대화하기 위한 기술적 방법론(예: 바늘의 종류 및 직경의 적절한 선택, 충분한 바늘천자횟수, 조직 획득 기술적 방법론, 검체 처리 방법), 시술 관련 합병증, 그리고 숙련도와 교육에 관련된 문제들에 대해 다루고 있다. 본 진료지침은 외부 전문가의 검토를 거쳤으며, 원고작성 시점까지 보고된 가능한 모든 최신 근거들에 기반하여 최선의 진료 방법을 권고하고 있다. 그러나 모든 임상 상황에 본 진료지침을 일괄적으로 적용할 수는 없으며, 기관의 법적/행정적 상황 및 환자의 개별 임상적 상황과 해당 자원의 가용성 등을 고려하여야 한다. 추후 내시경적 기술의 발전과 이로 인한 변화, 임상에서의 최신 근거를 토대로 본 진료지침이 개정될 수 있다.

High-entropy alloys have excellent mechanical properties under extreme environments, rendering them promising candidates for next-generation structural materials. It is desirable to develop non-equiatomic high-entropy alloys that do not require many expensive or heavy elements, contrary to the requirements of typical high-entropy alloys. In this study, a non-equiatomic high-entropy alloy powder Fe49.5Mn30Co10Cr10C0.5 (at.%) is prepared by high energy ball milling and fabricated by spark plasma sintering. By combining different ball milling times and ball-topowder ratios, we attempt to find a proper mechanical alloying condition to achieve improved mechanical properties. The milled powder and sintered specimens are examined using X-ray diffraction to investigate the progress of mechanical alloying and microstructural changes. A miniature tensile specimen after sintering is used to investigate the mechanical properties. Furthermore, quantitative analysis of the microstructure is performed using electron backscatter diffraction.

번식지에서 이소하여 분산한 유조의 이동 패턴과 서식지를 파악하는 것은 개체 보전과 관리를 위해 매우 중요하다. 노랑부리 백로는 국제적인 보호종으로 필리핀, 말레이시아, 대만 등지에서 월동하며, 중국, 러시아, 우리나라 서해 무인도서에서 번식한다. 본 연구에서는 2018년도와 2019년도에 영광 칠산도에서 번식하여 이소한 노랑부리백로 유조 총 6개체를 대상으로 야생동물위치추적장치를 부착하여 이소 후 하절기 동안 이동 경로 및 행동권 분석을 통해 주요 서식지 이용 양상을 파악하였다. 2018년도에 번식한 노랑부리백로 유조 3개체 중 CE1801 개체는 이소 후 북상을 하다가 다시 영광 백수 갯벌 지역으로 회귀하여 서식하였으며, 나머지 CE1802, CE1803 개체는 태안 지역으로 북상하여 서식하였다. 2019년도의 경우 CE1901 개체는 CE1801 개체와 유사한 패턴을 보였으며, CE1902 개체는 완도 지역으로 남하하여 서식하였고, CE1903 개체는 신안 지역으로 남하하다가 다시 영광 백수 갯벌 지역으로 회귀하여 핵심 행동권을 보였다. 본 연구에서 노랑부리백로 유조는 하절기 동안 안정적인 서식지를 찾기 위해 서해안 갯벌 지역을 중심으로 폭 넓게 이동을 하였다. 향후 노랑부리백로 유조가 이용하는 핵심 서식지에 대해 개발과 출입을 제한하는 등 서식지 보호를 위한 노력이 필요하다.

To cope with automobile exhaust gas regulations, ISG and charging control systems are applied to HEV vehicles for the purpose of improving fuel economy. These systems require quick charge-discharge performance of high current. Therefore, a Module of the AGM battery with high energy density and EDLC(Electric Double Layer Capacitor) with high power density are constructed to study the charging and discharging behavior. In CCA, which evaluates the starting performance at -18 oC & 30 oC with high current, EDLC contributed for about 8 sec at the beginning. At 0 oC CA (Charge Acceptance), the initial Charging current of the AGM/EDLC Module, is twice that of the AGM lead acid battery. To play the role of EDLC during high-current rapid charging and discharging, the condition of the AGM lead-acid battery is optimally maintained. As a result of a Standard of Battery Association of Japan (SBA) S0101 test, the service life of the Module of the AGM Lead Acid Battery/EDLC is found to improve by 2 times compared to that of the AGM Lead Acid Battery.

To cope with automobile exhaust gas regulations, ISG (Idling Stop & Go) and charging control systems are applied to HEVs (Hybrid Electric Vehicle) for the purpose of improving fuel economy. These systems require quick charge/discharge performance at high current. To satisfy this characteristic, improvement of the positive electrode plate is studied to improve the charge/discharge process and performance of AGM(Absorbent Glass Mat) lead-acid batteries applied to ISG automotive systems. The bonding between grid and A.M (Active Material) can be improved by applying the Sand-Blasting method to provide roughness to the surface of the positive grid. When the Sand-Blasting method is applied with conditions of ball speed 1,000 rpm and conveyor speed 5 M/min, ideal bonding is achieved between grid and A.M. The positive plate of each condition is applied to the AGM LAB (Absorbent Glass Mat Lead Acid Battery); then, the performance and ISG life characteristics are tested by the vehicle battery test method. In CCA, which evaluates the starting performance at -18 oC and 30 oC with high current, the advanced AGM LAB improves about 25 %. At 0 oC CA (Charge Acceptance), the initial charging current of the advanced AGM LAB increases about 25 %. Improving the bonding between the grid and A.M. by roughening the grid surface improves the flow of current and lowers the resistance, which is considered to have a significant effect on the high current charging/discharging area. In a Standard of Battery Association of Japan (SBA) S0101 test, after 300 A discharge, the voltage of the advanced AGM LAB with the Sand-Blasting method grid was 0.059 V higher than that of untreated grid. As the cycle progresses, the gap widens to 0.13 V at the point of 10,800 cycles. As the bonding between grid and A.M. increases through the Sand Blasting method, the slope of the discharge voltage declines gradually as the cycle progresses, showing excellent battery life characteristics. It is believed that system will exhibit excellent characteristics in the vehicle environment of the ISG system, in which charge/discharge occurs over a short time.

A well-established characterization method is required in powder bed fusion (PBF) metal additive manufacturing, where metal powder is used. The characterization methods from the traditional powder metallurgy process are still being used. However, it is necessary to develop advanced methods of property evaluation with the advances in additive manufacturing technology. In this article, the characterization methods of powders for metal PBF are reviewed, and the recent research trends are introduced. Standardization status and specifications for metal powder for the PBF process which published by the ISO, ASTM, and MPIF are also covered. The establishment of powder characterization methods are expected to contribute to the metal powder industry and the advancement of additive manufacturing technology through the creation of related databases.