Variation of Precipitation Behavior with Heat Treatment of Friction Stir Processed AA6082

Kim, JaeHwang,Song, Ram,Lee, KwangJin American Scientific Publishers 2017 Journal of nanoscience and nanotechnology Vol.17 No.6

<P>The extruded AA6082 was heat treated after friction stir processing (FSP) in this study. The grain size is affected by the friction heat during FSP. Smaller grain size is confirmed in the stir zone (SZ) than any other regions due to the dynamic recrystallization. Hardness is substantially enhanced during heat treatment after FSP. Hardness is highly fluctuated in the region of heat affected zone (HAZ) during aging process. The region of HAZ is divided into three regions called as HAZ1, HAZ2 and HAZ3 where the area of HAZ1, HAZ2 and HAZ3 is defined as the area close to SZ, middle of HAZ and close to base material (BM), respectively. The crystal structure of nano size precipitates is revealed using high resolution transmission electron microscope. The maximum hardness is obtained in base material region due to the formation of the beta '' phase with high number density. On the other hand, the minimum hardness is identified in HAZ2 since the grain is grown and the beta' phase is formed during FSP.</P>

Effect of Cu Contents on Nanocluster Formation and Two-Step Aging Behavior in Al–Mg–Si Alloys

MinYoung Song,InSu Kim,JaeHwang Kim,SungKil Hong 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.6

The effect of Cu contents on nanocluster formation and the two-step aging behavior of Al–Mg–Si alloys was studied based onhardness, DSC and TEM results. The activation energies for the formation of Cluster (1) were 61.6, 70.3 and 92.9 kJ/mol forCu-free, 1Cu (0.1 mass% Cu-added) and 3Cu (0.3 mass% Cu-added), respectively. It was confirmed that hardness increasedslowly with increasing Cu content during natural aging for 3.6 ks. These results suggest that the formation kinetics of Cluster(1) decrease due to the vacancy trapping phenomenon, because of the strong interactions of the Cu-vacancies. Meanwhile,the effect of the formation of nanoclusters by Cu addition on the two-step aging behavior at 170 °C during natural aging wasanalyzed. Hardness at the initial stage of the two-step aging increased with increasing Cu contents. This was caused by thesuppression of Cluster (1) formation during natural aging by the Cu additions. Based on TEM results, at the peak hardnessof the two-step aging, the number density of precipitates was increased by increasing Cu contents, due to the suppression ofnanocluster formation during natural aging.

Accuracy of Patient-Specific Instrument for Cylindrical Axis Implementation in Kinematically Aligned Total Knee Arthroplasty

Kwang-Kyoun Kim,Jaehwang Song 대한정형외과학회 2023 Clinics in Orthopedic Surgery Vol.15 No.5

Background: In kinematically aligned total knee arthroplasty (KA-TKA), the cylindrical axis (CA) is very important in restoring the native joint line and kinematics of the pre-arthritic knee. This study aimed to determine the accuracy of patient-specific instrument (PSI) for restoring the CA for femoral bone resection in KA-TKA. Methods: Thirty KA-TKAs were performed using a computed tomography (CT)-based PSI system. Data from preoperative CT were reconstructed into three-dimensional (3D) models using 3D-planning software. The CA was created by connecting the centers of each virtual sphere to the medial and lateral femoral condyles using computer software. Femoral bone resection of the distal and posterior condyles was performed parallel to the sagittal planes of the CA. The thickness of the CA-referenced bone resection was determined based on the thickness necessary for the respective regions of the femoral component. The PSI was manufactured to locate the guide pin for a conventional cutting block. The accuracy of PSI for KA-TKA was evaluated as the absolute error between the preoperatively predicted thickness and the intraoperative measurements in each of the four regions, as well as the difference in error between distal-medial (DM) and posterior-medial (PM) and between distal-lateral (DL) and posterior-lateral (PL). Results: The differences in thickness of bone cut in the DM, DL, PM, and PL were 0.79 ± 0.39 mm (range, –1.20 to 1.50), 0.70 ± 0.42 mm (range, –1.50 to 1.50), 0.80 ± 0.46 mm (range, –0.80 to 1.50), and 0.75 ± 0.47 mm (range, –2.10 to 1.40), respectively. There was no significant difference in the thickness error between DM and PM (p = 0.959) and between DL and PL (p = 0.812). Conclusions: In KA-TKA, PSI was effective for accurate femoral bone resection based on virtually planned thickness.

Infl uence of Natural Aging Time and Mg/Si Ratio (Mg + Si = 1.3 mass%) on the Two-Step Aging Behavior in Al–Mg–Si Alloys

JiWoo Im,JaeYeol Jeon,MinYoung Song,SungKil Hong,JaeHwang Kim 대한금속·재료학회 2019 METALS AND MATERIALS International Vol.25 No.4

Two-step aging with the diff erent natural aging times and chemical compositions was carried out in Al–Mg–Si alloys toinvestigate the clustering and two-step aging behavior. The activation energies of cluster formation through the Kissingermethod were analyzed as 69.4, 67.3 and 73.8 kJ/mol for the 9M4S, 6M6S and 3M10S, respectively. A similar hardnesswas identifi ed for short-term natural aging for 3.6 ks regardless of the Mg/Si ratio. On the other hand, a lower hardness wasidentifi ed in the 3M10S (Mg/Si = 0.3) than in 9M4S (Mg/Si = 2.5) and 6M6S (Mg/Si = 1) for long-term natural aging for4838.4 ks. The hardness increase during the two-step aging was due to the formation of a β″ phase during artifi cial agingbased on structure analysis of high resolution transmission electron microscope images. There was a hardness decrease atthe initial stage of the two-step aging at 170 °C in the case of long-term naturally-aged specimens. The hardness decreasewas caused by the partial dissolution of the Mg–Si co-cluster, which was infl uenced by the Mg/Si ratio. Meanwhile, the hardnessincrease during two-step aging was promoted for 6M6S and the higher number density of the β″ phase was confi rmed.

폭풍해일과 강우에 의한 해안 도시 범람 수치모의를 위한 우수관망 수치모형의 개발

윤성범(Yoon, Sung Bum),이재황(Lee, Jaehwang),김건형(Kim, Gun Hyeong),송지훈(Song, Ji Hoon) 한국해안해양공학회 2014 한국해안해양공학회 논문집 Vol.26 No.5

기존의 태풍에 의한 해안 범람 수치모의 연구의 대부분은 폭풍해일만을 고려하였으므로 강우에 의한 추가적인 침수는 배제되어 왔다. 일반적으로 태풍은 강우를 동반한 자연재해이므로 폭풍해일에 의한 해안 도시범람을 수치모의 하는 데 있어 반드시 강우의 영향이 고려되어야 한다. 또한 강우는 도시 우수 관망을 통해 바다로 배출되므로 강우를 동반하는 폭풍해일 수치모의 시 우수관망 시스템이 고려되어야 타당한 결과를 얻을 수 있다. 본 연구에서는 기존의 폭풍해일 수치모형에 강우와 우수관망을 해석할 수 있는 알고리즘을 추가하여 수치모형을 개발하였다. 개발된 수치모형을 단순화된 지형에 적용하여 강우에 의한 범람과 우수의 배수, 해수의 역류현상, 우수의 배수에 따른 해수면 상승 등 기본적인 수치모형의 기능을 검사하였다. 그 결과 다양한 조건에서 수치모형이 정상적으로 작동되는 것을 확인하였다. Since most of the researches on the coastal inundation due to typhoons have considered only storm surges, an additional inundation due to rainfall has been neglected. In general, typhoons are natural disasters being accompanied by the rainfall. Thus, it is essential to consider the effect of rainfall in the numerical simulation of coastal inundation due to storm surges. Because the rainwater is discharged to the sea through the storm sewer system, it should be included in the numerical simulation of storm surges to obtain reasonable results. In this study an algorithm that can deal with the effects of rainfall and sewer system is developed and combined with a conventional storm surge numerical model. To test the present numerical model various numerical simulations are conducted using the simplified topography for the cases including the inundation due to rainfall, the drainage of rainwater, the backflow of sea water, and the increase of sea water level due to drainage of rainwater. As a result, it is confirmed that the basic performance of the present model is satisfactory for various flow situations.

대장수술 후에 발생한 급성신부전의 위험인자

이혜미,황창재,김재황,김흥대,박대팔,서일숙,송선옥,김세연,이덕희,지대림 영남대학교 의과대학 2007 Yeungnam University Journal of Medicine Vol.24 No.2

연구 배경 : 급성 신부전은 술 후 발생할 수 있는 합병증 중에서 사망률은 큰 영향을 줄 수 있으므로 이 연구를 통해 위험인자를 알아보려고 한다. 재료 및 방법 : 2004년 1월부터 2006년 12월까지 3년간 영남대학교 의과대학 부속병원에서 대장 수술을 받은 570명의 환자들을 대상으로 하였다. 환자들의 성별과 연령, 미국 마취과학회 신체등급, 동반질환, 수술의 종류, 응급수술의 여부, 수술 시간, 재수술의 여부, 술 중의 투약 상황, 술 후에 자가 통증 조절기에 사용한 약제, 술 중에 저혈압의 유무, 수혈 여부, 술 후 기계적 환기를 시행한 경우를 비교하였다. 결과 : 비교 결과에서 성별과 수술의 종류, 응급 수술의 여부, 개복여부 등에는 유의한 차이를 보이지 않았다. 반면 환자의 나이와 수술 시간, 재수술의 여부, 술중에 이뇨제 등을 사용한 경우, 술 중에 저혈압의 유무, 술 후에 기계적 환기를 시행한 경우 등에는 유의한 차이를 보였다. 결론 : 이상의 결과로 급성신부전의 원인은 어느 한 가지라고 하기 보다는 위험인자에 얼마나 노출되어 있는가가 결정하는 것 같고, 그 원인들이 모여서 상승효과를 내는 것 같다. 그러므로 수술 전부터 많은 위험에 노출된 환자는 술 중 더 적극적인 감시를 시행하여 수술 후의 합병증 발생을 줄이는 노력을 기울여야 하겠다. Background : Acute renal failure is one of the leading causes of postoperative morbidity and mortality. The purpose of this study was to determine the risk factors that are associated with acute renal failure after colorectal surgery. Materials and Methods : Five hundred seventy patients who operated colorectal surgery at the Yeungnam University Medical Center over three years from 2004 to 2006 were enrolled in this study. The effects of gender, age, ASA classification, concomitant disease, surgery type and duration, reoperation, urogenital manipulation, medication, hypotension, hypovolemia, transfusion, and postoperative ventilatory care on the occurrence of acute renal failure after colorectal surgery were studied. Results : The major risk factors of acute renal failure after colorectal surgery were age of patients (P=0.003), ASA classification (P<0.001), concomitant disease (P<0.001), duration of the time surgery (P=0.034), reoperation (P=0.001), use of intraoperative diuretics (P=0.005), use of postoperative diuretics (P<0.001), intraoperative hypotension (P=0.018), intraoperative transfusion (P<0.001), postoperative transfusion (P<0.001), and postoperative ventilatory care (P=0.001). Conclusion : Multiple factors cause synergistic effects on the development of acute renal failure after colorectal surgery. Therefore, efforts to reduce the risk factors associated with acute renal failure are needed. In addition, intensive postoperative care should be provided to all patients.

거리 분포 특성에 근거한 터보 부호의 순환 조직형 컨벌루션 부호 설계

김대선(Dae-Son Kim),송홍엽(Hong-Yeop Song),이동학(Dong-Hahk Lee),유재황(Jaehwang Yu) 한국통신학회 2008 韓國通信學會論文誌 Vol.33 No.2c

본 논문에서 터보 부호의 성능을 최대화 시킬 수 있도록 구성 부호의 거리 분포 특성에 근거하여 구성 순환조직형 컨벌루션(RSC : recursive systematic convolutional) 부호를 설계 하는 방법을 제안한다. 부호율이 1/2인 RSC 부호에 대하여 컴퓨터로 검색하고 그 결과는 표로 정리하여 제시한다. 찾은 부호들의 성능은 컴퓨터 모의실험을 통해 검증한다. 제안된 방법으로 설계한 부호들은 반복 복호에 따른 빠른 수렴 정도를 보여주면서 좋은 성능을 가진다. In this letter, we propose a new design of recursive systematic convolutional (RSC) codes based on the distance spectrum properties which can maximize the performance. Good constituent RSC codes of code rate 1/2 are searched by computer and presented in a table. Their performances are shown by computer simulation. New designed codes shows faster convergences according to iterative decoding and good performances.

Epidemiology and Characteristics of Ankle and Foot Injuries in Electric Scooter-Related Accidents

Tae Gyun Kim,Jae Gyu Choi,Youn Moo Heo,Jin Woong Yi,In Uk Yeo,Hyun Sik Ryu,Hyun Soo Choi,Jaehwang Song 대한정형외과학회 2024 Clinics in Orthopedic Surgery Vol.16 No.2

Background: The use of electric scooters (e-scooters) continues to increase as a simple, inexpensive means of transport, resulting in a sharp increase in the incidence of scooter-related accidents. No study to date has closely examined the injury extent to the lower leg, joints, and extremities from e-scooter-related accidents. Here, we investigated the epidemiology and injury patterns of such accidents, focusing on injuries to the ankle and foot. Methods: Based on data from a single tertiary hospital’s database, the demographics of 563 patients with scooter-associated injuries were analyzed retrospectively. Among the patients, 229 patients who were injured by e-scooter riding were further investigated. Based on the data, the general demographics of whole scooter-associated injuries and the injury characteristics and fracture cases of the lower leg, ankle, and foot were analyzed. Results: During the 4-year study period, the number of patients injured by e-scooters increased every year. Lower extremities were the most common injury site (67.2%) among riders, whereas injuries to the head and neck (64.3%) were more common in riders of non-electric scooters. Among the lower leg, ankle, and foot injuries of riders (52 cases), the ankle joint (53.8%) was the most commonly injured site, followed by the foot (40.4%) and lower leg (21.2%). The fracture group scored significantly higher on the Abbreviated Injury Scale than the non-fracture group (p < 0.001). Among the fracture group (20 cases), ankle fractures (9 cases) were most common, including pronation external rotation type 4 injuries (4 cases) and pilon fractures (2 cases). Five patients (25%) had open fractures, and 12 patients (60%) underwent surgical treatment. Conclusions: The ankle and foot are the most common injury sites in e-scooter-related accidents. Given the high frequency and severity of e-scooter-related ankle and foot injuries, we suggest that more attention be paid to preventing these types of injuries with greater public awareness of the dangers of using e-scooters.