표면치밀화 기술에 의해 제조된 소결 기어의 기계적 특성

김기정,김기범,이두환,박종관,정동국,Kim, Ki-Jung,Kim, Ki-Bum,Lee, Doo-Hwan,Park, Jong-Kwan,Jeong, Dong-Guk 한국분말야금학회 2012 한국분말재료학회지 (KPMI) Vol.19 No.3

A novel PM (powder metallurgy) steel for automotive power-train gear components was developed to reduce manufacturing cost, while meeting application requirements. The high-density PM steel was manufactured by mixing using special Cr-Mo atomized iron powders, high-pressure compaction, and sintering. Tensile strength, charpy impact, bending fatigue, and contact fatigue tests for the PM steel were carried out and compared to conventional forged steel. Pinion gears for auto-transmission were also manufactured by helical pressing, sintering, and surface densification process. In order to evaluate the durability of the PM parts, auto-transmission durability tests were performed using dynamometer tests. Results showed that the PM steel fulfilled the requirements for pinion gears indicating suitable tensile, bending fatigue, contact fatigue strengths and improved gear tooth profile. The PM gears also showed good performance during the transmission durability tests. As a result, the PM gears showed significant potential to replace the conventional forged steel gears manufactured by tooth machining (hobbing, shaving, and grinding) processes.

척수내 종양과 감별을 요하는 비종양성 척수증 : 수술로 확진된 8례의 후향적 분석

김기정,정천기,심기범,김현집,Kim, Ki-Jeong,Chung, Chun-Kee,Sim, Ki-Bum,Kim, Hyun-Jib 대한신경외과학회 2000 Journal of Korean neurosurgical society Vol.29 No.7

Objective : It is difficult to differentiate intramedullary spinal cord tumors preoperatively from non-neoplastic pathologies in patients presenting as non-compressive myelopathies in magnetic resonance imaging(MRI). In this report, the authors reviewed nonneoplastic intramedullary spinal cord lesions preoperatively diagnosed as tumors and discussed their clinical and radiological characteristics and usefulness of surgical intervention. Methods : From January, 1985 to January, 1999, authors experienced eight non-neoplastic pathologies mimicking intramedullary spinal cord tumors and analysed their medical records, radiological findings and histopathological specimens retrospectively. Results : There were five males and three females and the duration of symptoms were from two to 20 months(mean, 9.8 months). The location of lesions were four cervical, one cervicothoracic and three thoracic. All patients manifested sensory abnormality, seven motor weakness, and six bladder symptom. All cases had swollen spinal cords and increased signal intensities in spin-echo sequences. Six cases showed contrast enhancement : four cases were focal and two diffuse. Under the impression of intramedullary tumors, the patients were operated upon. Final diagnoses on the base of clinical and pathologic finding were : three subacute necrotizing myelopathies, two multiple scleroses, two myelopathy of unknown etiology. One case showed no gross abnormality in surgical field in spite of adequate exposure of the lesion, so biopsy was not performed. In that case, postoperative MRI revealed spontaneous resolution of the lesion. Conclusion : MRI is invaluable diagnostic tool in screening myelopathies. However, its high sensitivity and lack of specificity make difficulty in preoperative differential diagnosis of non-compressive myelopathies. Although no surgical morbidity occurred in our series, we sometimes failed to confirm definite diagnosis even with biopsy. In such a circumstance, long-term follow up is needed.

테레프탈레이트계 폴리에스터의 열분해 거동에 관한 연구

김기정,여정섭,윤지영,김준호,Kim Ki Jeong,Yeo Jeong Sup,Yoon Ji Young,Kim Joon Ho 한국섬유공학회 2005 한국섬유공학회지 Vol.42 No.4

Thermal degradation behavior of the three homologous polyesters, poly(ethylene terephthalate)(PET), poly(trimethylene terephthalate)(PTT) and poly(butylene terephthalate)(PBT) were investigated by using thermogravimetric analysis(TGA) and pyrolysis-gas chromatography-mass spectrometry(PGC-MS). From the results of isothermal thermogravimetry, it was revealed that PTT has higher activation energy of thermal degradation than the other two polyesters. In PGC-MS analysis, the highly volatile products of the polyesters such as acetaldehyde and acetic acid evolved in the early stage of pyrolysis as common degradation products. Benzoic acid, methyl ester of benzoic acid, terephthalic acid and higher oligomers were produced as the main degradation products of poly(alkylene terephthalate)s at longer pyrolysis times. In isothermal pyrolysis, PTT showed the fastest thermal degradation rate among the three polyesters.

A Study on the Mitigation of the Exposure Dose Applying Bolus Tracking in Brain Perfusion CT Scan

김기정,정홍량,임청환,홍동희,심재구,유인규,Kim, Ki-Jeong,Jung, Hong-Ryang,Lim, Cheong-Hwan,Hong, Dong-Hee,Shim, Jae-Goo,You, In-Gyu The Society of Digital Policy and Management 2014 디지털융복합연구 Vol.12 No.3

급성기 허혈성 뇌졸중 증상이 있는 뇌 관류 CT 검사를 시행한 환자를 대상으로 장비사가 제시한 고정 시간 기법(Fixed time technique)과 조영제 추적 기법(Bolus tracking technique)을 비교하여 환자의 피폭선량을 분석하고자 하였으며, 조영제 추적 기법의 유용성과 최적의 조영증강 구간을 구현하는 Time graph를 알아보기 위한 것이다. 환자에서는 PCT의 $CTDI_{VOL}$은 고정시간기법에서 431.72mGy, Bolus tracking에서 323.61mGy로 측정되었고, DLP값은 고정시간기법에서 $1243.47mGy{\cdot}cm$, Bolus tracking에서 $932mGy{\cdot}cm$로 측정되었다. Time graph는 고정시간기법에서 다양하게 나타났으나, Bolus tracking 기법에서는 최적의 Time graph를 얻을 수 있었으며, 뇌 관류 CT검사 시 Bolus tracking기법을 적용하여 피폭선량을 25% 정도 감소시킬 수 있었다. This study was conducted to analyze the patient's exposed dose targeting the patients who had acute ischemic stroke symptoms and CT brain perfusion scan, by comparing fixed time technique and bolus tracking technique which was provided by the manufacturer and to identify the Time graph to implement the usability of contrast medium's tracking technique the best contrast enhancement intervals. $CTDI_{VOL}$ of PCT in patient appeared to be 431.72mGy in fixed scan delay protocol, whereas 323.61mGy in Bolus tracking technique. The value of DLP appeared to be $1243.47mGy{\cdot}cm$ in fixed scan delay protocol, whereas $932mGy{\cdot}cm$ in Bolus tracking technique. Time graph appeared to be various in fixed scan delay protocol, whereas the optimal time graph could be obtained in Bolus tracking. The exposure dose could be reduced by 25% applying Bolus tracking technique when taking brain perfusion CT scan.

전산화단층촬영검사실 방사선사의 방사선피폭 방어행위에 영향을 미치는 요인 분석

김기정,정홍량,홍동희,Kim, Ki-Jeong,Jung, Hong-Ryang,Hong, Dong-Hee 대한방사선과학회 2018 방사선기술과학 Vol.41 No.6

This study was conducted to analyze factors Influencing Protective Behavior against Radiation Exposure using questionnaires for 231 radiological technologists working in Computed Tomography(CT) examination room with high radiation dose in diagnostic radiology field. Statistical analysis of the collected data revealed that the reasons for partially shielding the examination part in the CT scan were the lack of protective equipment, securing of radiation justification, being annoying and maybe not being harm to adults in order. It was also revealed that the variables influencing the protective behavior were protective behavior against radiation harm, self-efficacy, protective environment, organization culture, protective knowledge and protective instrument in order. The higher the radiological protective environment(${\beta}=0.245$) and the lower the radiological protective knowledge(${\beta}=-0.034$), the more influential the protective behavior against radiation harm was. In this study, it was shown that non examination parts were not shielded in the CT scan. Therefore, it is necessary to improve the level of protective environment, to cultivate knowledge to improve the protective behavior against radiation harm and to have an intervention strategy for concrete action.

단결정 그라핀 위에서의 퓨란의 고리모양 형성

김기정,양세나,박영찬,이한구,김봉수,이한길,Kim, Ki-Jeong,Yang, Se-Na,Park, Young-Chan,Lee, Han-Koo,Kim, Bong-Soo,Lee, Han-Gil 한국진공학회 2011 Applied Science and Convergence Technology Vol.20 No.4

본 연구 그룹은 6H-SiC (0001)에서 성장시킨 그라핀 층에 흡착된 퓨란(furan)의 고리 형성과 전자적 성질을 원자 힘 현미경(Atomic Force Microscope : AFM), C K-edge에 대한 Near Edge X-ray Absorption Fine Structure (NEXAFS) 스펙트럼, 핵심부 준위 광전자 분광스펙트럼(Core-level Photoemission Spectroscopy : CLPES)을 이용하여 연구했다. 우리는 그라핀위에 흡착된 퓨란 분자들이 화학적 도핑이 가능한 산소기의 홀 전자쌍을 통하여 그라핀의 특성을 조절할 수 있는 화학적 기능화에 이용될 수 있다는 것을 알아냈다. 또한, 퓨란이 자발적으로 세 가지의 다른 결합 구조들 중 하나로 고리를 형성한다는 것과 그라핀 위에 퓨란에 의해 형성된 고리의 전자적 성질들이 AFM, NEXAFS, CLPES를 이용하여 각각 설명될 수 있다는 것을 보여주었다. The ring formation and electronic properties of furan adsorbed on graphene layers grown on 6H-SiC (0001) has been investigated using atomic force microscopy (AFM), near edge X-ray absorption fine structure (NEXAFS) spectra for the C K-edge, and core level photoemission spectroscopy (CLPES). Moreover, we observed that furan molecules adsorbed on graphene could be used for chemical functionalization via the lone pair electrons of the oxygen group, allowing chemical doping. We also found that furan spontaneously form rings with one of three different bonding configurations and the electronic properties of the ring formed by furan on graphene can be described using by AFM, NEXAFS and CLPES, respectively.

저상굴절버스의 전 차륜 조향 시스템 ECU 개발에 대한 연구

김기정,이수호,정기현,최경희,박태원,문경호,Kim, Ki-Jeong,Lee, Soo-Ho,Chung, Ki-Hyun,Choi, Kyung-Hee,Park, Tae-Won,Moon, Kyeong-Ho 한국정보처리학회 2010 정보처리학회논문지 A Vol.17 No.1

삶의 질이 높아지고 고령화 사회가 시작되면서, 사회적 약자들이 사용하기 쉬운 교통수단의 개발의 필요성이 증대되고 있다. 이러한 요구에 부응하기 위해, 한국철도기술연구원에서 주관하여 저상굴절버스(Bi-modal Tram)의 개발을 시작하게 되었다. 이 저상굴절버스는 버스와 같은 높은 접근성의 특징을 가져야 할 뿐만 아니라, 지하철과 같이 차체가 낮아야 하며, 휠체어나 승객의 발이 승강장과 차량 사이 틈에 끼지 않도록 정확한 주차가 이루어져야 한다. 하지만 저상굴절차량의 길이가 길어, 이러한 요건을 맞추기 위해서는 전 차륜 조향 시스템이 개발-장착되어야 한다. 전 차륜 조향 시스템이 장착된 저상굴절차량은 1축 차륜이 조향될 뿐 아니라, 1축 조향각 또는 굴절각과 속도 등의 상태에 따라 2축과 3축 차륜이 조향되는 특징을 가지고 있다. 본 연구에서는 전 차륜 조향장치의 개발 과정을 다룬다. As standard of living is higher and aging society is coming, it is needed to develop transportation that is easy to use for weak person. To comply with the demands, it is started to make Bi-modal Tram that is on KRRI(Korea Railroad Research Institute)'s hands. This tram has to have good accessibility like bus, be low level from ground like subway, and park accurately so wheel chair's or passenger's foot can't fall into the gap. But Bi-modal Tram have long length, so it need development of All Wheel Steering System. The Bi-modal Tram that have all wheel steering system steer not only the first axle but also the second and third axle from the first axle or articulation angle, and velocity, and so on. At this study, we discuss AWS ECU's development process.

킬른더스트를 사용한 콘크리트의 강도 및 내구특성에 관한 연구

김기정 ( Kim¸ Ki-jeong ),차천수 ( Lee¸ Yong Sung ),김성수 ( Li¸ Bai Shou ),손성운 ( Yoon¸ Gi-won ),한천구 ( Han¸ Cheon-goo ) 한국구조물진단유지관리공학회 2003 한국구조물진단유지관리공학회 학술발표대회 논문집 Vol.7 No.1

In this study, the properties of fresh and hardened concrete, and durability are discussed when cement kiln dust is replaced for cement and fine aggregate. According to the results, slump and air content of concrete, in which CKD is used, decreases remarkably due to an increase of viscosity and filling of the pores. Compressive strength increases due to filling of the pores and reduction of air content in comparison with plain concrete. In the case of replacement of CKD for fine aggregate, drying shrinkage and neutralizing depth of concrete show the similar tendency to plain concrete, but in the case of replacement of CKD for cement, they increase in comparison with plain concrete. When CKD is used in concrete, relative dynamic elastic modulus diminishes in all case due to reduction of air content.

킬른더스트를 사용한 콘크리트의 강도 및 내구특성에 관한 연구

김기정(Kim Ki-Jeong),차천수(Lee Yong Sung),김성수(Li Bai Shou),손성운(Yoon Gi-Won),한천구(Han Cheon-Goo) 한국구조물진단유지관리학회 2003 한국구조물진단학회 학술발표회논문집 Vol.- No.-

In this study, the properties of fresh and hardened concrete, and durability are discussed when cement kiln dust is replaced for cement and fine aggregate. According to the results, slump and air content of concrete, in which CKD is used, decreases remarkably due to an increase of viscosity and filling of the pores. Compressive strength increases due to filling of the pores and reduction of air content in comparison with plain concrete. In the case of replacement of CKD for fine aggregate, drying shrinkage and neutralizing depth of concrete show the similar tendency to plain concrete, but in the case of replacement of CKD for cement, they increase in comparison with plain concrete. When CKD is used in concrete, relative dynamic elastic modulus diminishes in all case due to reduction of air content.

지구성 트레드밀 운동이 모체감염으로 유발된 뇌성마비 쥐의 운동기능, 정서기능 및 인지기능에 미치는 영향

김기정 ( Ki Jeong Kim ),서진희 ( Jin Hee Seo ),김보균 ( Bo Kyun Kim ),김대영 ( Dae Young Kim ),성윤희 ( Yun Hee Sung ),김창주 ( Chang Ju Kim ),진현지 ( Hyun Ji Jin ),김영표 ( Young Pyo Kim ) 한국운동생리학회 2009 운동과학 Vol.18 No.3