Effect of Ultrasonic Melt Treatment on Solidification Microstructure of Al–5Ti–1B Alloy Containing Numerous Inoculant Particles

Soo‑Bae Kim,Jae‑Gil Jung,Young‑Hee Cho,Su‑Hyeon Kim,Kwangjun Euh,Jung‑Moo Lee 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.7

The effect of ultrasonic melt treatment (UST) on the solidification microstructure of an Al–5Ti–1B alloy containing highvolumefractions of Al3Tiand TiB2particles is investigated for various UST times with different melt holding times. Theas-cast Al–5Ti–1B alloy is composed of TiB2and polygonal Al3Tiparticles (present prior to UST), plate-like Al3Tiparticles,and Al grains (formed during UST and/or solidification). The UST causes a size reduction and homogeneous distributionof the TiB2-agglomerated region containing many submicron-sized TiB2particles pushed to the grain boundaries. The USTslightly decreases the size and improves the distribution of polygonal Al3Tiparticles enriched in the TiB2-agglomeratedregion. Unlike the TiB2and polygonal Al3Tiparticles, which exhibit a minor refining effect, the plate-like Al3Tiparticlesshow a significant refinement with UST application. The UST has a significant effect on the size distribution of Al grains byinducing the formation of medium-sized grains at the expense of small and large grains; however, it only has a slight effecton grain refinement. The degree of microstructure modification increases with increasing UST time but decreases with meltholding time after UST. The mechanisms for the refinement and dispersion of the TiB2and Al3Tiparticles and Al grains arediscussed considering fragmentation, nucleation, and growth behaviors induced by the UST and subsequent solidification.

모래다짐말뚝 개량폭에 따른 보강효과에 관한 연구

김시운,정길수,박병수,유남재 江原大學校 産業技術硏究所 2005 産業技術硏究 Vol.25 No.A

In this research, centrifuge model experiments and numerical approach of finite element method to analyze experimental results were performed to investigate the behavior of improved ground with sand compaction piles. One of typical clay minerals, kaolinite powder, were prepared for soft ground in model tests. Jumunjin standard sand was used to sand compaction pile installed in the soft soil. In order to investigate the characteristics of mechanical behavior of sand compaction piles with low replacement ratios, centrifuge model experiments with the replacement ratio of 40%, changing the width of improved area with respect to testing results the width of surcharge loads, were carried out to obtain of bearing capacity, characteristics of load-settlement, vertical stresses acting on the sand pile and the soft soil failure mechanism in improved ground.

가상여행 시스템 연구

김승찬,최성,신정길 호서대학교 반도체제조장비국산화연구센터 2001 반도체장비학술심포지움 Vol.2001 No.-

본 논문은 인터넷의 발달로 가능해진 가상현실의 구현과 가상현실세계에서의 자아를 대신한 아바타(AVATAR)를 이용하여 가상 여행 System 설계에 대해서 연구하였다.가상현실(Virtual Reality) 기술은 컴퓨터 그래픽을 이용하여 가상세계(Virtual World)를 구현하고 아바타를 이용하여 인간이 실제로 여행하는것과 같은 몰입감을 부여하는 것이 목적이다.더 나아가서 인간의 시각을 통해 전해지는 영상을 이용하여 가상현실을 조정함으로서 현실에서 인간이 느끼는 상태를 가상세계에 적용하여 더욱 완벽한 현실 대체를 연구하였다.

발열이 있는 호중구 감소증 환자에서의 위험도 예측인자

정중식,권운용,김규석,임용수,이중의,서길준,윤여규 대한응급의학회 2000 대한응급의학회지 Vol.11 No.3

Background: Most febrile neutropenic patients are treated in an aggressive manner. However, identification of low-risk patients may enable clinicians to administer risk-based treatment. The object of this study is to certify the factors associated with increased risk at the time of visiting the emergency department. Methods: This is a retrospective study. We reviewed the medical records of 101 febrile neutropenic patients who had visited the emergency department of Seoul National University Hospital from January 1998 to August 1999. We assumed 22 risk prediction factors that could be assessed at admission to the emergency department and 5 factors that could be assessed during treatment course. To find independent risk-prediction factors, we analyzed these factors respectively by using multiple regression analysis. Results: Tachycardia(aOR=136.5), altered mentality(aOR=28.8), decreased renal function(aOR=20.1), and significant comorbidity(aOR=17,2) are the independent factors associated with higher mortality. Altered mentality(aOR=31.6) and decreased renal function(CCr < 75㎖/min, aOR=5.4) are those associated with a higher incidence of septic shock. Independent factors associated with persistent(more than 3 days) fever are the early(within 10 days) onset of fever after last chemotherapy(aOR=8.8) and the existence of new pulmonary infiltrates on a simple chest X-ray(aOR=4.3). Conclusion: The stability of vital signs, the change of mentality, the renal function, the existence of significant comorbidity, the existence of new pulmonary infiltrates, and the rate of neutropenia are clinically useful risk-prediction factors in febrile neutropenia at the time of visiting the emergency department.

지도자의 경쟁가치리더십과 선수만족 및 인지된 경기력의 관계

김종욱,양용길,이정수,장갑석,정종환 한국스포츠리서치 2004 한국 스포츠 리서치 Vol.15 No.3

The purpose of this study was to identify the relationships among competing value leadership, athlete satisfaction and performance in sport field, The instrument for data collection was a questionnaire in which competing value leadership consisted as identified by Ha(1996), athlete satisfaction consisted as identified by Che(1997), and performance consisted as identified by An(2002), 350 subjects were selected from universities in Seoul by the stratified cluster sampling method, Among these selected subjects, 322 responded, and data analyses consisted of employing descriptive statistics, one-way ANOVA, multiple-regression using SPSS/PC version 11.0. First, competing value leadership and athlete satisfaction differ statistically and partially according to socio-demographic variables of athletes, Second, athlete satisfaction and performance statistically and significantly is influenced by competing value leadership of leader, Third, athlete satisfaction statistically and significantly influence performance of athletes.

황국균과 백국균의 대두 코지제조중 키토산의 효과

정순택,문길만,조건식,강성국,김설희 木浦大學校 工業技術硏究所 1998 工業技術硏究誌 Vol.8 No.-

The effect of chitosan in soybean koji preparation and characteristics of chitosan-koji were investigated. Aspergillus oryzae KCTC 6096 and Aspergillus kawachii KCCM 11458 was used for koji preparation. a-Amylase activity of soybean koji prepared with 0.25% 10cp chitosan was excellent relative to 30 cp chitosan and 1.6 times higher than non-added soybean koji. Acid and neutral protease activities of soybean koji prepared with 0.25%, 10 cp chitosan were showed simillary higher value than non-chitosna added koji. The period of koji preperation was reduced 30% by adding chitosan.

모바일 로봇의 견실제어를 위한 제네틱 알고리즘 개발

김홍래,배길호,정경규,한성현 한국공작기계학회 2004 한국공작기계학회 춘계학술대회논문집 Vol.2004 No.-

This paper proposed trajectory tracking control of mobile robot. Trajectory tracking control scheme are real coding genetic-algorithm and back-propergation algorithm. Control scheme ability experience proposed simulation. Stable tracking control problem of mobile robots have been studied in recent years. These studies have guaranteed stability of controller, but the performance of transient state has not been guaranteed. In some situations, constant gain controller shows overshoots and oscillations. So we introduce better control scheme using Real coding Genetic Algorithm(RCGA) and neural network. Using RCGA, we can find proper gains in several situations and these gains are generalized by neural network. The generalization power of neural network will give proper gain in untrained situation. Performance of proposed controller will verify numerical simulations and the results show better performance than constant gain controller.

Delay Line을 이용한 1차 미분 임펄스 발생기 설계

김은정,임재현,김길겸,김학선 한밭대학교 정보통신전문대학원 2004 정보통신전문대학원 논문집 Vol.2 No.1

본 논문에서는 UWB (Ultra-WideBand)시스템에 사용되는 짧은 폭의 임펄스 발생기를 설계하였다. SRD와 두개의 단락된 전송 선로를 이용 하였다. 단락된 전송 선로는 시간 지연과 위상의 반전을 효과적으로 제공 한다. RC 미분기 대신에 단락된 전송 선로(Delay Line)을 이용하여 1차 미분 임펄스를 발생시켰다. 시뮬레이션을 통해 700psec의 펄스폭과 600mV(p.p)의 진폭, 펄스 모양의 좋은 대칭성을 확인하였고 또한, 펄스 주변의 떨림 현상이 거의 발생하지 않았다. In this paper, we have designed impulse generator of short pulse width for UWB(Ultra-Wide band) system using SRD and two short-circuited stubs. The short-circuited stub provides good time delay and reverse of phase. The first derivative impulse was generated by using short-circuited stub(Delay Line) instead of RC differentiator. A first derivative impulse of 700 psec pulse duration, 600mV(p.p) pulse amplitued, and good symmetry has been demonstrated though simulation. Also, there are extremely small amount of ringing around the first derivative impulse.

생쥐의 강제수영시 부동자세시간과 통각예민도간의 상관관계

김길중,박제민,김명정 大韓神經精神醫學會 1991 신경정신의학 Vol.30 No.4

The purpose of the study is to test by an animal experiment the hypothesis that pain insensitivity in depression is a trait marker rather than a state marker. 39 mice were studied for pain sensitivity by means of tail flick test before and after 6 minutes of forced swimming and for total duration of immobility during the last 4 minutes of forced swimming. The correlation coefficients were calculated among the basal pain sensitivity, the change of pain sensitivity after forced swimming and duration of immobility during the forced swimming. The results are as follows. 1) A significant positive correlation was proved between the degree of pain insensitivity and duration of immobility during forced swimming. 2) The forced swimming induced a significant pain insensitivity and a significant negative correlation was shown between duration of immobility and the change of pain sensitivity after forced swimming. From these results, the author suggests that pain insensitivity in depression may be a trait marker rather than a state marker depending on the state of depression itself.

사이클론 내부의 유동특성에 관한 연구

김대욱,윤완중,손현철,박길문 朝鮮大學校 機械技術硏究所 2000 機械技術硏究 Vol.3 No.2

For manufacturing the small-type incinerator with collecting performance of high efficiency, the experimental study was carried out with considering cyclone characteristics, tangential velocity, radial velocity and pressure of the internal cyclone. The model cyclone consisted of slick acryl was made for similarity and data of tangential inflow velocity were acquired by using a vinyl particle as a working fluid. The results obtained from the experimentation are summarized as follows : 1. Tangential velocity of internal cyclone increases as the size of particle become bigger 2. Pressure is maximum value at the wall of cyclone and decreases toward the center of cyclone. 3. The difference of pressure between maximum and minimum value is increased as the size of particle become bigger.