The Ti-6Al-4V lattice structure is widely used in the aerospace industry owing to its high specific strength, specific stiffness, and energy absorption. The quality, performance, and surface roughness of the additively manufactured parts are significantly dependent on various process parameters. Therefore, it is important to study process parameter optimization for relative density and surface roughness control. Here, the part density and surface roughness are examined according to the hatching space, laser power, and scan rotation during laser-powder bed fusion (LPBF), and the optimal process parameters for LPBF are investigated. It has high density and low surface roughness in the specific process parameter ranges of hatching space (0.06–0.12 mm), laser power (225–325 W), and scan rotation (15°). In addition, to investigate the compressive behavior of the lattice structure, a finite element analysis is performed based on the homogenization method. Finite element analysis using the homogenization method indicates that the number of elements decreases from 437,710 to 27 and the analysis time decreases from 3,360 to 9 s. In addition, to verify the reliability of this method, stress–strain data from the compression test and analysis are compared.

Recently, considerable attention has been given to nickel-based superalloys used in additive manufacturing. However, additive manufacturing is limited by a slow build rate in obtaining optimal densities. In this study, optimal volumetric energy density (VED) was calculated using optimal process parameters of IN718 provided by additive manufacturing of laser powder-bed fusion. The laser power and scan speed were controlled using the same ratio to maintain the optimal VED and achieve a fast build rate. Cube samples were manufactured using seven process parameters, including an optimal process parameter. Analysis was conducted based on changes in density and melt-pool morphology. At a low laser power and scan speed, the energy applied to the powder bed was proportional to and not . At a high laser power and scan speed, a curved track was formed due to Plateau-Rayleigh instability. However, a wide melt-pool shape and continuous track were formed, which did not significantly affect the density. We were able to verify the validity of the VED formula and succeeded in achieving a 75% higher build rate than that of the optimal parameter, with a slight decrease in density and hardness.

This study investigates the effect of process stopping and restarting on the microstructure and local nanoindentation properties of 316L stainless steel manufactured via selective laser melting (SLM). We find that stopping the SLM process midway, exposing the substrate to air having an oxygen concentration of 22% or more for 12 h, and subsequently restarting the process, makes little difference to the density of the restarted area (~ 99.8%) as compared to the previously melted area of the substrate below. While the microstructure and pore distribution near the stop/restart area changes, this modified process does not induce the development of unusual features, such as an inhomogeneous microstructure or irregular pore distribution in the substrate. An analysis of the stiffness and hardness values of the nano-indented steel also reveals very little change at the joint of the stop/restart area. Further, we discuss the possible and effective follow-up actions of stopping and subsequently restarting the SLM process.

Ti-6Al-4V alloy has a wide range of applications, ranging from turbine blades that require smooth surfaces for aerodynamic purposes to biomedical implants, where a certain surface roughness promotes biomedical compatibility. Therefore, it would be advantageous if the high volumetric density is maintained while controlling the surface roughness during the LPBF of Ti-6Al-4V. In this study, the volumetric energy density is varied by independently changing the laser power and scan speed to document the changes in the relative sample density and surface roughness. The results where the energy density is similar but the process parameters are different are compared. For comparable energy density but higher laser power and scan speed, the relative density remained similar at approximately 99%. However, the surface roughness varies, and the maximum increase rate is approximately 172%. To investigate the cause of the increased surface roughness, a nonlinear finite element heat transfer analysis is performed to compare the maximum temperature, cooling rate, and lifetime of the melt pool with different process parameters.

본 연구에서는 가물치(Channa argus) 추출물의 신경세포 분화와 산화 스트레스에서의 효능을 분석하기 위하여 녹차와 효소를 이용한 다양한 추출 방법(상온 추출물, RE; 녹차 상온 추출물, GRE; 효소 상온 추출물, ERE; 녹차 효소 상온 추출물, GERE)을 사용하여 제조 된 추출물의 아미노산 조성과 항산화 활성을 비교 분석하였고, 신경성장인자 (NGF) 유도 신경세포 분화 및 과산화수소 처리에 의해 유도된 PC12 세포 독성에 대한 보호효과를 규명하고자 하였다. 총 아미노산 함량은 RE 및 GRE보다 효소 추출물인 ERE 및 GERE에서 훨씬 더 높았다. 효소 가수 분해물 (ERE 및 GERE)에서 ABTS 라디칼 소거 활성은 RE 및 GRE보다 높았다. 또한, RE와 ERE는 PC12 세포에서 neuronal growth factor (NGF) 매개 신경 돌기 성장뿐만 아 니라 growth associated protein (GAP)-43 및 synapsin-1의 발현을 현저하게 향상 시켰다. 과산화수소(H2O2)에 의해 손 상된 PC12 세포에 4가지 유형의 Channa argus 추출물을 첨가한 후 PC12 세포의 생존율을 측정하였다. PC12 세포 의 생존율은 RE, GRE, GERE에서 각각 77.5±1.9%, 84.0±0.8%, 81.1±0.9%이였다. 이러한 세포 생존율은 H2O2 만을 처리 한 음성 대조군(70.0±2.0%)에 비해 더 높았다. H2O2 처리에 의해 유도 된 세포 독성도 RE, GRE 및 GERE 처리에 대한 반응으로 상당히 완화되었다. 종합하면, Channa argus 추출물은 산화 스트레스와 신경 손상을 감소시키는 기능성 물질로 유용하다는 것을 시사하며, 향후 이들 소재를 활용한 다양한 기능성 제품의 개발이 필요할 것으로 판단된다.

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.

Powder characteristics, such as density, size, shape, thermal properties, and surface area, are of significant importance in the powder bed fusion (PBF) process. The powder required is exclusive for an efficient PBF process. In this study, the particle size distribution suitable for the powder bed fusion process was derived by modeling the PBF product using simulation software (GeoDict). The modeling was carried out by layering sintered powder with a large particle size distribution, with 50 μm being the largest particle size. The results of the simulation showed that the porosity decreased when the mean particle size of the powder was reduced or the standard deviation increased. The particle size distribution of prepared titanium powder by the atomization process was also studied. This study is expected to offer direction for studies related to powder production for additive manufacturing.

본 연구에서는 α-glucosidase 저해활성이 우수한 천연 자원을 개발하기 위하여 개똥쑥으로부터 천연 물질을 분리·동정하고 분리된 물질에 대하여 α-glucosidase 저해활성을 측정하였다. 개똥쑥 잎과 줄 기의 chloroform층과 ethyl acetate층으로부터 각각 6개와 5개의 화합물을 분리하였다. 분리한 화합물 중 chloroform층으로부터 분리된 ArteCA(M.W. 316g/mol, C16H12O7)는 isorhamnetin, ArteCB(M.W. 360g/mol, C18H16O8)는 chrysosplenol D, ArteCC(M.W. 316 g/mol, C16H12O7)는 rhamnetin, ArteCD (M.W. 374g/mol, C18H16O8)는 chrysosplenetin, ArteCE(M.W. 284g/mol, C21H20O12)는 acacetin 그리 고 ArteCF(M.W. 270g/mol, C16H14O4)는 imperatorin으로 확인되었다. 한편 EtOAc층으로부터 분리된 ArteEAA(M.W. 178g/mol, C9H6O4)는 6,7-dihydroxy coumarin, ArteEAB (M.W. 192g/mol, C10H8O4) 는 scopoletin, ArteEAC (M.W. 448g/mol, C21H20O11)는 kaempferol-3-O-b-D-glucoside, ArteEAD (M.W. 464 g/mol, C21H20O12)는 quercetin-3-O-b-D-glucoside 및 ArteEAE(M.W. 318g/mol, C15H10O8)는 myricetin으로 확인되었다. 이 중에서 ArteEAE(myricetin)는 α-glucosidase에 대하여 97.3%의 높은 저해활성을 가지고 있었으므로, 혈당조절용 건강식품 또는 치료제 개발을 위한 물질로 활용될 수 있을 것으로 판단되었다.

정부는 해양환경복원과 수산자원을 회복하기 위해 1971년부터 2014년까지 약 44년 동안 222,627ha의 인공어초어장 을 조성하였다. 그러나 인공어초 설치사업은 증가되고 있는 반면 아직까지 설치된 어초의 효과에 대한 연구는 부족한 실정이다. 이에 본 연구에서는 포항시 장길리 해역에 설치된 뿔삼각형어초에 부착·서식하는 저서동물의 시간적 군집변 화를 살펴보기 위해 2003년 포항시 장길리 해역 수심 5∼7m에 설치된 뿔삼각형어초를 대상으로 2009년 2월부터 2011년 8월까지 총 4회에 걸쳐 어초에 부착된 저서동물의 군집을 분석하였다. 그 결과 우점하는 분류군은 연체동물이고 우점종은 바다방석고둥인 것으로 나타났다. 또한 출현종들은 대부분 시공간의 변화에 따라 달라지는 양상을 보였다. 따라서 이 연구를 통해 시설해역과 목적하는 종의 특성에 적합한 인공어초 개발 연구, 사후관리에 관한 이용, 관리제도 제정 등에 활용될 것으로 기대한다.

In South Korea, the total root production volume of Platycodon grandiflorum was 5,255ton in 1991 but it rapidly decreased to about 50% (2,697 ton) in 2002. From 2006, however, it has beengradually increased and reached to 6,759 ton in 2011. Meantime, the imported root of Platycodon grandi-florum for the pharmaceutical purpose was 429 ton in 2001 but it has been dramatically decreased to 36ton in 2011. Instead, the imported volume of dried or fresh one for food was 11,652 ton in 2008 andremained at similar level up to now. Although the volume was very little (less than 23 ton), Platycodongrandiflorum's root cultivated in South Korea has also been exported to China, Japan and several coun-tries. Gyeongnam province in South Korea produced 1,100 ton of Platycodon grandiflorum's root in 2010and Geochang gun produced the largest volume (743 ton). Recently, the cultivation area is continuallyincreased in Hapcheon and Sancheong-Gun. We predict that the total production volume of Platycodongrandiflorum's root in South Korea will be continually increased in future due to consumer's continuousdemands and a rising unit price.

Biochar amendment to agricultural soil is regarded as a promising option to mitigateclimate change and enhance soil quality. It could sequester more carbon within the soil systemand increase plant yield by changing soil physicochemical characteristics. However, sustainableuse of biochar requires comprehensive environmental assessment. In this sense, it is important tomeasure additional greenhouse gas emission from soils after biochar addition. We investigatedemissions of CO2, N2O, and CH4from incubated soils collected from rice paddy and cultivatedgrassland after amendment of 3% biochar(wt.) produced from rice chaff. During incubation,soils were exposed to three wet-dry cycles ranging from 5~~85% soil gravimetric water content(WC) to investigate the changes in effect of biochar when influenced by different water levels. TheCO2emission was reduced in biochar treatment compared to the control at WC of 30~~70% bothin rice paddy and grassland soils. This indicates that biochar could function as a stabilizer for soilorganic carbon and it can be effective in carbon sequestration. The N2O emission was alsoreduced from the grassland soil treated with biochar when WC was greater than 30% because thebiochar treated soils had lower denitrification due to better aeration. In the rice paddy soil,biochar addition resulted in decrease in N2O emission when WC was greater than 70%, while anincrease was noted when WC was between 30~~70%. This increase might be related to the factthat available nutrients on biochar surface stimulated existing nitrifying bacterial community,resulting in higher N2O emission. Overall results imply that biochar amendment to agriculturalsoil can stabilize soil carbon from fast decomposition although attention should be paid toadditional N2O emission when biochar addition is combined with the application of nitrogenfertilizer.

본 시험은 젖소 4두에 대하여 제1위체류형 센서(Indwelling probe)를 정치시키고 이를 이용하여 아급성제1위과산증 (SARA)의 강도를 조사함과 동시에 pH가 혈 중 내독소 (Lipopolysaccharide; LPS)의 농도에 미치는 효과를 알아보 기 위하여 수행되었다. 비섬유성탄수화물(Non-fiber carbohydrates, NFC)을 기준으로 적정 수준의 NFC를 포함하고 있는 정상 사료군(Normal diet, ND)과, 아급성제1위과산증 (Subacute ruminal acidosis, SARA) 유발가능 사료군(Acidogenic diet, AD)의 2개 처리구에 각 2두씩 배치하여 Cross-over 설계로 사양실험을 반복 실시하였다. 제1위체류형 센서는 장시간에 걸친 제1위 내 pH의 변화를 추적하는 데 효과적 이었다. 얻어진 결과에서 AD 급여는 반추위내용물의 pH를 낮추는 데 커다란 영향을 주었으며, 반추위 내 pH의 저하 는 혈 중 LPS의 농도가 증가로 이어짐을 확인할 수 있었 다. 따라서 혈 중 LPS 농도는 급성 또는 만성형을 불문하 고 과산증을 확인하는 지표로 사용 가능할 것으로 판단된다. 또한 착유우용 사료첨가물로 많이 이용되는 소디움벤 토나이트(NaB)와 프로필렌글리콜(PG)의 급여는 반추위 내 pH의 저하를 완충시켜 궁극적으로 SARA의 강도를 완화시 키고 혈 중 Lipopolysaccharides (LPS) 농도의 증가를 줄여 줌으로써 내독소에 의해 발생하기 쉬운 제엽염 등의 부작 용을 완화시키는 데 도움을 줄 수 있을 것으로 사료된다.

This paper reviewed the relationship between job satisfaction and service quality, and the moderating effect of gender in restaurant employee. Based on the responses from 288 employees, the results of multiple regression analysis showed that intrinsic job satisfaction(JS) and extrinsic job satisfaction effect positively on all service quality factors(tangibles, reliability, responsiveness, empathy). The results of moderating analysis showed that intrinsic JS effects positively on all service quality factors irrespective of gender, but the positive effect of extrinsic JS on tangibles and empathy is more positive in female than in male employee.

본 연구에서는 국내에서 유통되고 있는 청국장을 수집하고 품질 특성을 분석하였으며, 우수한 품질의 청국장 제조를 위한 종균 개발의 기초 자료로 활용하고자 한다. 먼저 국내에서 시판 되는 청국장을 수집하여 분석한 결과, 수분함량은 56.3∼62.1%, 염도는 0.23∼11.51%, 총질소 함량과 아미노태 질소 함량은 각각 5.82∼8.76%, 173.71∼2,700.66 mg%를 나타내었다. 총질소에 대한 아미노태 질소 함량의 비를 나타내는 질소분해율은 2.88∼26.93%를 나타내었다. 수집된 청국장의 최대 히스타민과 티라민 함량은 각각 755.40, 1913.51 mg/kg로 나타냈다. 청국장의 최대 생균수는 9.6 × 109 CFU/g이었다. 이상의 결과로 국내 청국장은 종류가 매우 다양하며 제품마다 풍미와 영양성분이 현저한 차이가 있음을 확인하였다. 이는 지역마다 다른 품종의 원료대두의 사용 및 균일화·체계화되지 못한 발효공정에 기인한 것이라 사료된다.